diff --git a/src/odr/internal/pdf/pdf_cmap_parser.cpp b/src/odr/internal/pdf/pdf_cmap_parser.cpp
index c28934bc..99264cb5 100644
--- a/src/odr/internal/pdf/pdf_cmap_parser.cpp
+++ b/src/odr/internal/pdf/pdf_cmap_parser.cpp
@@ -13,13 +13,13 @@ static constexpr int_type eof = std::streambuf::traits_type::eof();
 
 CMapParser::CMapParser(std::istream &in) : m_parser(in) {}
 
-std::istream &CMapParser::in() const { return m_parser.in(); }
+std::istream &CMapParser::in() { return m_parser.in(); }
 
-std::streambuf &CMapParser::sb() const { return m_parser.sb(); }
+std::streambuf &CMapParser::sb() { return m_parser.sb(); }
 
-const ObjectParser &CMapParser::parser() const { return m_parser; }
+const ObjectParser &CMapParser::parser() { return m_parser; }
 
-std::variant<Object, std::string> CMapParser::read_token() const {
+std::variant<Object, std::string> CMapParser::read_token() {
   if (m_parser.peek_number()) {
     return std::visit([](auto n) { return Object(n); },
                       m_parser.read_integer_or_real());
@@ -51,7 +51,7 @@ std::variant<Object, std::string> CMapParser::read_token() const {
 }
 
 void CMapParser::read_codespacerange(const std::uint32_t n,
-                                     [[maybe_unused]] const CMap &cmap) const {
+                                     [[maybe_unused]] const CMap &cmap) {
   m_parser.skip_whitespace();
   for (std::uint32_t i = 0; i < n; ++i) {
     auto from_glyph = m_parser.read_object();
@@ -63,7 +63,7 @@ void CMapParser::read_codespacerange(const std::uint32_t n,
   }
 }
 
-void CMapParser::read_bfchar(const std::uint32_t n, CMap &cmap) const {
+void CMapParser::read_bfchar(const std::uint32_t n, CMap &cmap) {
   m_parser.skip_whitespace();
   for (std::uint32_t i = 0; i < n; ++i) {
     std::string glyph = m_parser.read_object().as_string();
@@ -88,7 +88,7 @@ void CMapParser::read_bfchar(const std::uint32_t n, CMap &cmap) const {
 }
 
 void CMapParser::read_bfrange(const std::uint32_t n,
-                              [[maybe_unused]] const CMap &cmap) const {
+                              [[maybe_unused]] const CMap &cmap) {
   m_parser.skip_whitespace();
   for (std::uint32_t i = 0; i < n; ++i) {
     auto from_glyph = m_parser.read_object();
@@ -102,7 +102,7 @@ void CMapParser::read_bfrange(const std::uint32_t n,
   }
 }
 
-CMap CMapParser::parse_cmap() const {
+CMap CMapParser::parse_cmap() {
   CMap cmap;
 
   std::uint32_t last_int{};
diff --git a/src/odr/internal/pdf/pdf_cmap_parser.hpp b/src/odr/internal/pdf/pdf_cmap_parser.hpp
index c7653257..8adb331e 100644
--- a/src/odr/internal/pdf/pdf_cmap_parser.hpp
+++ b/src/odr/internal/pdf/pdf_cmap_parser.hpp
@@ -16,20 +16,20 @@ class CMapParser {
 
   explicit CMapParser(std::istream &);
 
-  std::istream &in() const;
-  std::streambuf &sb() const;
-  const ObjectParser &parser() const;
+  [[nodiscard]] std::istream &in();
+  [[nodiscard]] std::streambuf &sb();
+  [[nodiscard]] const ObjectParser &parser();
 
-  CMap parse_cmap() const;
+  [[nodiscard]] CMap parse_cmap();
 
 private:
   ObjectParser m_parser;
 
-  Token read_token() const;
+  [[nodiscard]] Token read_token();
 
-  void read_codespacerange(std::uint32_t n, const CMap &) const;
-  void read_bfchar(std::uint32_t n, CMap &) const;
-  void read_bfrange(std::uint32_t n, const CMap &) const;
+  void read_codespacerange(std::uint32_t n, const CMap &cmap);
+  void read_bfchar(std::uint32_t n, CMap &cmap);
+  void read_bfrange(std::uint32_t n, const CMap &cmap);
 };
 
 } // namespace odr::internal::pdf
diff --git a/src/odr/internal/pdf/pdf_document.hpp b/src/odr/internal/pdf/pdf_document.hpp
index f926ccaf..48fc2a26 100644
--- a/src/odr/internal/pdf/pdf_document.hpp
+++ b/src/odr/internal/pdf/pdf_document.hpp
@@ -9,7 +9,7 @@ struct Catalog;
 struct Element;
 
 struct Document {
-  Catalog *catalog;
+  Catalog *catalog{nullptr};
   std::vector<std::unique_ptr<Element>> elements;
 
   template <typename T, typename... Args> T *create_element(Args &&...args) {
diff --git a/src/odr/internal/pdf/pdf_document_element.hpp b/src/odr/internal/pdf/pdf_document_element.hpp
index 264fc039..2578ea9f 100644
--- a/src/odr/internal/pdf/pdf_document_element.hpp
+++ b/src/odr/internal/pdf/pdf_document_element.hpp
@@ -44,7 +44,7 @@ struct Pages final : Element {
 struct Page final : Element {
   Pages *parent{nullptr};
 
-  Resources *resources;
+  Resources *resources{nullptr};
   std::vector<Annotation *> annotations;
 
   // TODO remove
diff --git a/src/odr/internal/pdf/pdf_document_parser.cpp b/src/odr/internal/pdf/pdf_document_parser.cpp
index 04e9e5ed..29cbe02f 100644
--- a/src/odr/internal/pdf/pdf_document_parser.cpp
+++ b/src/odr/internal/pdf/pdf_document_parser.cpp
@@ -167,9 +167,9 @@ Catalog *parse_catalog(DocumentParser &parser, const ObjectReference &reference,
 
 DocumentParser::DocumentParser(std::istream &in) : m_parser(in) {}
 
-std::istream &DocumentParser::in() const { return m_parser.in(); }
+std::istream &DocumentParser::in() { return m_parser.in(); }
 
-const FileParser &DocumentParser::parser() const { return m_parser; }
+FileParser &DocumentParser::parser() { return m_parser; }
 
 const Xref &DocumentParser::xref() const { return m_xref; }
 
diff --git a/src/odr/internal/pdf/pdf_document_parser.hpp b/src/odr/internal/pdf/pdf_document_parser.hpp
index 479bfe32..ced1a40b 100644
--- a/src/odr/internal/pdf/pdf_document_parser.hpp
+++ b/src/odr/internal/pdf/pdf_document_parser.hpp
@@ -15,8 +15,8 @@ class DocumentParser {
 public:
   explicit DocumentParser(std::istream &);
 
-  [[nodiscard]] std::istream &in() const;
-  [[nodiscard]] const FileParser &parser() const;
+  [[nodiscard]] std::istream &in();
+  [[nodiscard]] FileParser &parser();
   [[nodiscard]] const Xref &xref() const;
 
   const IndirectObject &read_object(const ObjectReference &reference);
diff --git a/src/odr/internal/pdf/pdf_file_parser.cpp b/src/odr/internal/pdf/pdf_file_parser.cpp
index 91492c4b..e1c3a362 100644
--- a/src/odr/internal/pdf/pdf_file_parser.cpp
+++ b/src/odr/internal/pdf/pdf_file_parser.cpp
@@ -10,13 +10,13 @@ namespace odr::internal::pdf {
 
 FileParser::FileParser(std::istream &in) : m_parser(in) {}
 
-std::istream &FileParser::in() const { return m_parser.in(); }
+std::istream &FileParser::in() { return m_parser.in(); }
 
-std::streambuf &FileParser::sb() const { return m_parser.sb(); }
+std::streambuf &FileParser::sb() { return m_parser.sb(); }
 
-const ObjectParser &FileParser::parser() const { return m_parser; }
+ObjectParser &FileParser::parser() { return m_parser; }
 
-IndirectObject FileParser::read_indirect_object() const {
+IndirectObject FileParser::read_indirect_object() {
   IndirectObject result;
 
   result.reference.id = m_parser.read_unsigned_integer();
@@ -47,7 +47,7 @@ IndirectObject FileParser::read_indirect_object() const {
   throw std::runtime_error("expected stream");
 }
 
-Trailer FileParser::read_trailer() const {
+Trailer FileParser::read_trailer() {
   m_parser.expect_characters("trailer");
   m_parser.skip_whitespace();
 
@@ -62,7 +62,7 @@ Trailer FileParser::read_trailer() const {
   return result;
 }
 
-Xref FileParser::read_xref() const {
+Xref FileParser::read_xref() {
   if (const std::string line = m_parser.read_line(); line != "xref") {
     throw std::runtime_error("expected xref");
   }
@@ -94,7 +94,7 @@ Xref FileParser::read_xref() const {
   }
 }
 
-StartXref FileParser::read_start_xref() const {
+StartXref FileParser::read_start_xref() {
   if (const std::string line = m_parser.read_line(); line != "startxref") {
     throw std::runtime_error("expected startxref");
   }
@@ -108,7 +108,7 @@ StartXref FileParser::read_start_xref() const {
   return result;
 }
 
-std::string FileParser::read_stream(const std::int32_t size) const {
+std::string FileParser::read_stream(const std::int32_t size) {
   std::string result;
 
   if (size >= 0) {
@@ -140,7 +140,7 @@ std::string FileParser::read_stream(const std::int32_t size) const {
   return result;
 }
 
-void FileParser::read_header() const {
+void FileParser::read_header() {
   const std::string header1 = m_parser.read_line();
   const std::string header2 = m_parser.read_line();
 
@@ -151,7 +151,7 @@ void FileParser::read_header() const {
   m_parser.skip_whitespace();
 }
 
-Entry FileParser::read_entry() const {
+Entry FileParser::read_entry() {
   std::uint32_t position = in().tellg();
   const std::string entry_header = m_parser.read_line();
   in().seekg(position);
@@ -179,7 +179,7 @@ Entry FileParser::read_entry() const {
   throw std::runtime_error("unknown entry");
 }
 
-void FileParser::seek_start_xref(const std::uint32_t margin) const {
+void FileParser::seek_start_xref(const std::uint32_t margin) {
   in().seekg(0, std::ios::end);
   const std::int64_t size = in().tellg();
   in().seekg(std::max(static_cast<std::int64_t>(0), size - margin),
diff --git a/src/odr/internal/pdf/pdf_file_parser.hpp b/src/odr/internal/pdf/pdf_file_parser.hpp
index 550d1a84..677a51e6 100644
--- a/src/odr/internal/pdf/pdf_file_parser.hpp
+++ b/src/odr/internal/pdf/pdf_file_parser.hpp
@@ -17,21 +17,21 @@ class FileParser {
 public:
   explicit FileParser(std::istream &);
 
-  [[nodiscard]] std::istream &in() const;
-  [[nodiscard]] std::streambuf &sb() const;
-  [[nodiscard]] const ObjectParser &parser() const;
+  [[nodiscard]] std::istream &in();
+  [[nodiscard]] std::streambuf &sb();
+  [[nodiscard]] ObjectParser &parser();
 
-  [[nodiscard]] IndirectObject read_indirect_object() const;
-  [[nodiscard]] Trailer read_trailer() const;
-  [[nodiscard]] Xref read_xref() const;
-  [[nodiscard]] StartXref read_start_xref() const;
+  [[nodiscard]] IndirectObject read_indirect_object();
+  [[nodiscard]] Trailer read_trailer();
+  [[nodiscard]] Xref read_xref();
+  [[nodiscard]] StartXref read_start_xref();
 
-  [[nodiscard]] std::string read_stream(std::int32_t size) const;
+  [[nodiscard]] std::string read_stream(std::int32_t size);
 
-  void read_header() const;
-  [[nodiscard]] Entry read_entry() const;
+  void read_header();
+  [[nodiscard]] Entry read_entry();
 
-  void seek_start_xref(std::uint32_t margin = 64) const;
+  void seek_start_xref(std::uint32_t margin = 64);
 
 private:
   ObjectParser m_parser;
diff --git a/src/odr/internal/pdf/pdf_graphics_operator.hpp b/src/odr/internal/pdf/pdf_graphics_operator.hpp
index 84efdb60..1b57c963 100644
--- a/src/odr/internal/pdf/pdf_graphics_operator.hpp
+++ b/src/odr/internal/pdf/pdf_graphics_operator.hpp
@@ -103,7 +103,7 @@ struct GraphicsOperator {
   using Argument = Object;
   using Arguments = std::vector<Argument>;
 
-  GraphicsOperatorType type;
+  GraphicsOperatorType type{GraphicsOperatorType::unknown};
   Arguments arguments;
 };
 
diff --git a/src/odr/internal/pdf/pdf_graphics_operator_parser.cpp b/src/odr/internal/pdf/pdf_graphics_operator_parser.cpp
index a6b27efa..7621f05d 100644
--- a/src/odr/internal/pdf/pdf_graphics_operator_parser.cpp
+++ b/src/odr/internal/pdf/pdf_graphics_operator_parser.cpp
@@ -115,11 +115,11 @@ static constexpr int_type eof = std::streambuf::traits_type::eof();
 GraphicsOperatorParser::GraphicsOperatorParser(std::istream &in)
     : m_parser(in) {}
 
-std::istream &GraphicsOperatorParser::in() const { return m_parser.in(); }
+std::istream &GraphicsOperatorParser::in() { return m_parser.in(); }
 
-std::streambuf &GraphicsOperatorParser::sb() const { return m_parser.sb(); }
+std::streambuf &GraphicsOperatorParser::sb() { return m_parser.sb(); }
 
-std::string GraphicsOperatorParser::read_operator_name() const {
+std::string GraphicsOperatorParser::read_operator_name() {
   std::string result;
 
   while (true) {
@@ -137,7 +137,7 @@ std::string GraphicsOperatorParser::read_operator_name() const {
   }
 }
 
-GraphicsOperator GraphicsOperatorParser::read_operator() const {
+GraphicsOperator GraphicsOperatorParser::read_operator() {
   GraphicsOperator result;
 
   while (true) {
diff --git a/src/odr/internal/pdf/pdf_graphics_operator_parser.hpp b/src/odr/internal/pdf/pdf_graphics_operator_parser.hpp
index 1cc337f8..3adf02a1 100644
--- a/src/odr/internal/pdf/pdf_graphics_operator_parser.hpp
+++ b/src/odr/internal/pdf/pdf_graphics_operator_parser.hpp
@@ -4,22 +4,18 @@
 
 namespace odr::internal::pdf {
 
-class SimpleArray;
-class SimpleArrayElement;
-class GraphicsArgument;
-enum class GraphicsOperatorType;
 struct GraphicsOperator;
 
 class GraphicsOperatorParser {
 public:
   explicit GraphicsOperatorParser(std::istream &);
 
-  [[nodiscard]] std::istream &in() const;
-  [[nodiscard]] std::streambuf &sb() const;
+  [[nodiscard]] std::istream &in();
+  [[nodiscard]] std::streambuf &sb();
 
-  [[nodiscard]] std::string read_operator_name() const;
+  [[nodiscard]] std::string read_operator_name();
 
-  [[nodiscard]] GraphicsOperator read_operator() const;
+  [[nodiscard]] GraphicsOperator read_operator();
 
 private:
   ObjectParser m_parser;
diff --git a/src/odr/internal/pdf/pdf_graphics_state.hpp b/src/odr/internal/pdf/pdf_graphics_state.hpp
index 11a7b066..6e4ea9e0 100644
--- a/src/odr/internal/pdf/pdf_graphics_state.hpp
+++ b/src/odr/internal/pdf/pdf_graphics_state.hpp
@@ -69,7 +69,7 @@ struct GraphicsState {
   GraphicsState();
 
   State &current();
-  const State &current() const;
+  [[nodiscard]] const State &current() const;
 
   void execute(const GraphicsOperator &);
 };
diff --git a/src/odr/internal/pdf/pdf_object_parser.cpp b/src/odr/internal/pdf/pdf_object_parser.cpp
index d7ba953e..dc81a567 100644
--- a/src/odr/internal/pdf/pdf_object_parser.cpp
+++ b/src/odr/internal/pdf/pdf_object_parser.cpp
@@ -12,11 +12,11 @@ namespace odr::internal::pdf {
 ObjectParser::ObjectParser(std::istream &in)
     : m_in{&in}, m_se(in, true), m_sb{in.rdbuf()} {}
 
-std::istream &ObjectParser::in() const { return *m_in; }
+std::istream &ObjectParser::in() { return *m_in; }
 
-std::streambuf &ObjectParser::sb() const { return *m_sb; }
+std::streambuf &ObjectParser::sb() { return *m_sb; }
 
-ObjectParser::int_type ObjectParser::geti() const {
+ObjectParser::int_type ObjectParser::geti() {
   const int_type c = sb().sgetc();
   if (c == eof) {
     in().setstate(std::ios::eofbit);
@@ -24,7 +24,7 @@ ObjectParser::int_type ObjectParser::geti() const {
   return c;
 }
 
-ObjectParser::char_type ObjectParser::getc() const {
+ObjectParser::char_type ObjectParser::getc() {
   const int_type c = sb().sgetc();
   if (c == eof) {
     in().setstate(std::ios::eofbit);
@@ -33,7 +33,7 @@ ObjectParser::char_type ObjectParser::getc() const {
   return static_cast<char_type>(c);
 }
 
-ObjectParser::char_type ObjectParser::bumpc() const {
+ObjectParser::char_type ObjectParser::bumpc() {
   const int_type c = sb().sbumpc();
   if (c == eof) {
     in().setstate(std::ios::eofbit);
@@ -42,7 +42,7 @@ ObjectParser::char_type ObjectParser::bumpc() const {
   return static_cast<char_type>(c);
 }
 
-std::string ObjectParser::bumpnc(const std::size_t n) const {
+std::string ObjectParser::bumpnc(const std::size_t n) {
   std::string result(n, '\0');
   if (const auto m = static_cast<std::streamsize>(n);
       sb().sgetn(result.data(), m) != m) {
@@ -51,7 +51,7 @@ std::string ObjectParser::bumpnc(const std::size_t n) const {
   return result;
 }
 
-void ObjectParser::ungetc() const {
+void ObjectParser::ungetc() {
   if (sb().sungetc() == eof) {
     throw std::runtime_error("unexpected stream exhaust");
   }
@@ -90,12 +90,12 @@ bool ObjectParser::is_whitespace(const char c) {
          c == ' ';
 }
 
-bool ObjectParser::peek_whitespace() const {
+bool ObjectParser::peek_whitespace() {
   const int_type c = geti();
   return c != eof && is_whitespace(static_cast<char_type>(c));
 }
 
-void ObjectParser::skip_whitespace() const {
+void ObjectParser::skip_whitespace() {
   while (true) {
     const int_type c = geti();
     if (c == eof) {
@@ -108,14 +108,14 @@ void ObjectParser::skip_whitespace() const {
   }
 }
 
-void ObjectParser::skip_line() const { read_line(); }
+void ObjectParser::skip_line() { read_line(); }
 
-std::string ObjectParser::read_line(const bool inclusive) const {
+std::string ObjectParser::read_line(const bool inclusive) {
   return util::stream::read_line(in(), inclusive);
 }
 
-void ObjectParser::expect_characters(const std::string &string) const {
-  auto observed = bumpnc(string.size());
+void ObjectParser::expect_characters(const std::string &string) {
+  const std::string observed = bumpnc(string.size());
   if (observed != string) {
     throw std::runtime_error("unexpected characters"
                              " (expected: " +
@@ -123,12 +123,12 @@ void ObjectParser::expect_characters(const std::string &string) const {
   }
 }
 
-bool ObjectParser::peek_number() const {
+bool ObjectParser::peek_number() {
   const int_type c = geti();
   return c != eof && (c == '+' || c == '-' || c == '.' || std::isdigit(c));
 }
 
-UnsignedInteger ObjectParser::read_unsigned_integer() const {
+UnsignedInteger ObjectParser::read_unsigned_integer() {
   UnsignedInteger result = 0;
 
   while (true) {
@@ -144,7 +144,7 @@ UnsignedInteger ObjectParser::read_unsigned_integer() const {
   }
 }
 
-Integer ObjectParser::read_integer() const {
+Integer ObjectParser::read_integer() {
   Integer sign = 1;
 
   const char_type c = getc();
@@ -160,11 +160,11 @@ Integer ObjectParser::read_integer() const {
   return sign * static_cast<Integer>(read_unsigned_integer());
 }
 
-Real ObjectParser::read_number() const {
+Real ObjectParser::read_number() {
   return std::visit([](auto v) -> Real { return v; }, read_integer_or_real());
 }
 
-std::variant<Integer, Real> ObjectParser::read_integer_or_real() const {
+std::variant<Integer, Real> ObjectParser::read_integer_or_real() {
   Integer i = 0;
 
   if (char_type c = getc(); c != '.') {
@@ -184,12 +184,12 @@ std::variant<Integer, Real> ObjectParser::read_integer_or_real() const {
          static_cast<Real>(i2) * std::pow(10.0, begin - end);
 }
 
-bool ObjectParser::peek_name() const {
+bool ObjectParser::peek_name() {
   const int_type c = geti();
   return c == '/';
 }
 
-void ObjectParser::read_name(std::ostream &out) const {
+void ObjectParser::read_name(std::ostream &out) {
   if (const char_type c = bumpc(); c != '/') {
     throw std::runtime_error("not a name");
   }
@@ -200,7 +200,7 @@ void ObjectParser::read_name(std::ostream &out) const {
     if (i == eof) {
       return;
     }
-    auto c = static_cast<char_type>(i);
+    const auto c = static_cast<char_type>(i);
     if (c < 0x21 || c > 0x7e || c == '/' || c == '%' || c == '(' || c == ')' ||
         c == '<' || c == '>' || c == '[' || c == ']' || c == '{' || c == '}') {
       return;
@@ -208,7 +208,7 @@ void ObjectParser::read_name(std::ostream &out) const {
 
     if (c == '#') {
       bumpc();
-      auto hex = bumpnc<2>();
+      const std::array hex = bumpnc<2>();
       out.put(two_hex_to_char(hex[0], hex[1]));
       continue;
     }
@@ -218,28 +218,28 @@ void ObjectParser::read_name(std::ostream &out) const {
   }
 }
 
-Name ObjectParser::read_name() const {
+Name ObjectParser::read_name() {
   std::stringstream ss;
   read_name(ss);
   return Name(ss.str());
 }
 
-bool ObjectParser::peek_null() const {
+bool ObjectParser::peek_null() {
   const int_type c = geti();
   return c != eof && (c == 'n' || c == 'N');
 }
 
-void ObjectParser::read_null() const {
+void ObjectParser::read_null() {
   std::ignore = bumpnc<4>();
   // TODO check ignore case
 }
 
-bool ObjectParser::peek_boolean() const {
+bool ObjectParser::peek_boolean() {
   const int_type c = geti();
   return c != eof && (c == 't' || c == 'T' || c == 'f' || c == 'F');
 }
 
-Boolean ObjectParser::read_boolean() const {
+Boolean ObjectParser::read_boolean() {
   const int_type c = geti();
 
   if (c == 't' || c == 'T') {
@@ -259,7 +259,7 @@ Boolean ObjectParser::read_boolean() const {
   throw std::runtime_error("unexpected starting character");
 }
 
-bool ObjectParser::peek_string() const {
+bool ObjectParser::peek_string() {
   int_type c = geti();
   if (c == eof) {
     return false;
@@ -276,7 +276,7 @@ bool ObjectParser::peek_string() const {
   return false;
 }
 
-std::variant<StandardString, HexString> ObjectParser::read_string() const {
+std::variant<StandardString, HexString> ObjectParser::read_string() {
   std::string string;
 
   char_type c = bumpc();
@@ -288,7 +288,7 @@ std::variant<StandardString, HexString> ObjectParser::read_string() const {
       if (c == '\\') {
         c = getc();
         if (std::isdigit(c)) {
-          auto octet = bumpnc<3>();
+          const std::array octet = bumpnc<3>();
           string += three_octet_to_char(octet[0], octet[1], octet[2]);
         } else {
           bumpc();
@@ -320,12 +320,12 @@ std::variant<StandardString, HexString> ObjectParser::read_string() const {
   throw std::runtime_error("unexpected starting character");
 }
 
-bool ObjectParser::peek_array() const {
+bool ObjectParser::peek_array() {
   const int_type c = geti();
   return c == '[';
 }
 
-Array ObjectParser::read_array() const {
+Array ObjectParser::read_array() {
   Array::Holder result;
 
   if (bumpc() != '[') {
@@ -356,7 +356,7 @@ Array ObjectParser::read_array() const {
   }
 }
 
-bool ObjectParser::peek_dictionary() const {
+bool ObjectParser::peek_dictionary() {
   const int_type i = geti();
   if (i == eof) {
     return false;
@@ -370,7 +370,7 @@ bool ObjectParser::peek_dictionary() const {
   return false;
 }
 
-Dictionary ObjectParser::read_dictionary() const {
+Dictionary ObjectParser::read_dictionary() {
   Dictionary::Holder result;
 
   if (bumpc() != '<') {
@@ -411,7 +411,7 @@ Dictionary ObjectParser::read_dictionary() const {
   }
 }
 
-Object ObjectParser::read_object() const {
+Object ObjectParser::read_object() {
   getc();
 
   if (peek_null()) {
@@ -442,7 +442,7 @@ Object ObjectParser::read_object() const {
   throw std::runtime_error("unknown object");
 }
 
-ObjectReference ObjectParser::read_object_reference() const {
+ObjectReference ObjectParser::read_object_reference() {
   UnsignedInteger id = read_unsigned_integer();
   skip_whitespace();
   UnsignedInteger gen = read_unsigned_integer();
diff --git a/src/odr/internal/pdf/pdf_object_parser.hpp b/src/odr/internal/pdf/pdf_object_parser.hpp
index 16925a58..a67e5ec5 100644
--- a/src/odr/internal/pdf/pdf_object_parser.hpp
+++ b/src/odr/internal/pdf/pdf_object_parser.hpp
@@ -18,21 +18,21 @@ class ObjectParser {
 
   explicit ObjectParser(std::istream &);
 
-  [[nodiscard]] std::istream &in() const;
-  [[nodiscard]] std::streambuf &sb() const;
+  [[nodiscard]] std::istream &in();
+  [[nodiscard]] std::streambuf &sb();
 
-  int_type geti() const;
-  char_type getc() const;
-  char_type bumpc() const;
-  template <std::uint32_t N> std::array<char, N> bumpnc() const {
+  int_type geti();
+  char_type getc();
+  char_type bumpc();
+  template <std::uint32_t N> std::array<char, N> bumpnc() {
     std::array<char, N> result;
     if (sb().sgetn(result.data(), result.size()) != result.size()) {
       throw std::runtime_error("unexpected stream exhaust");
     }
     return result;
   }
-  [[nodiscard]] std::string bumpnc(std::size_t n) const;
-  void ungetc() const;
+  std::string bumpnc(std::size_t n);
+  void ungetc();
 
   static int_type octet_char_to_int(char_type c);
   static int_type hex_char_to_int(char_type c);
@@ -41,45 +41,45 @@ class ObjectParser {
                                        char_type third);
 
   static bool is_whitespace(char c);
-  [[nodiscard]] bool peek_whitespace() const;
-  void skip_whitespace() const;
-  void skip_line() const;
-  std::string read_line(bool inclusive = false) const;
-  void expect_characters(const std::string &string) const;
+  [[nodiscard]] bool peek_whitespace();
+  void skip_whitespace();
+  void skip_line();
+  std::string read_line(bool inclusive = false);
+  void expect_characters(const std::string &string);
 
-  [[nodiscard]] bool peek_number() const;
-  [[nodiscard]] UnsignedInteger read_unsigned_integer() const;
-  [[nodiscard]] Integer read_integer() const;
-  [[nodiscard]] Real read_number() const;
-  [[nodiscard]] std::variant<Integer, Real> read_integer_or_real() const;
+  [[nodiscard]] bool peek_number();
+  [[nodiscard]] UnsignedInteger read_unsigned_integer();
+  [[nodiscard]] Integer read_integer();
+  [[nodiscard]] Real read_number();
+  [[nodiscard]] std::variant<Integer, Real> read_integer_or_real();
 
-  [[nodiscard]] bool peek_name() const;
-  void read_name(std::ostream &) const;
-  [[nodiscard]] Name read_name() const;
+  [[nodiscard]] bool peek_name();
+  void read_name(std::ostream &);
+  [[nodiscard]] Name read_name();
 
-  [[nodiscard]] bool peek_null() const;
-  void read_null() const;
+  [[nodiscard]] bool peek_null();
+  void read_null();
 
-  [[nodiscard]] bool peek_boolean() const;
-  [[nodiscard]] Boolean read_boolean() const;
+  [[nodiscard]] bool peek_boolean();
+  [[nodiscard]] Boolean read_boolean();
 
-  [[nodiscard]] bool peek_string() const;
-  [[nodiscard]] std::variant<StandardString, HexString> read_string() const;
+  [[nodiscard]] bool peek_string();
+  [[nodiscard]] std::variant<StandardString, HexString> read_string();
 
-  [[nodiscard]] bool peek_array() const;
-  [[nodiscard]] Array read_array() const;
+  [[nodiscard]] bool peek_array();
+  [[nodiscard]] Array read_array();
 
-  [[nodiscard]] bool peek_dictionary() const;
-  [[nodiscard]] Dictionary read_dictionary() const;
+  [[nodiscard]] bool peek_dictionary();
+  [[nodiscard]] Dictionary read_dictionary();
 
-  [[nodiscard]] Object read_object() const;
+  [[nodiscard]] Object read_object();
 
-  [[nodiscard]] ObjectReference read_object_reference() const;
+  [[nodiscard]] ObjectReference read_object_reference();
 
 private:
-  std::istream *m_in;
+  std::istream *m_in{nullptr};
   std::istream::sentry m_se;
-  std::streambuf *m_sb;
+  std::streambuf *m_sb{nullptr};
 };
 
 } // namespace odr::internal::pdf
diff --git a/test/src/internal/pdf/pdf_file_parser.cpp b/test/src/internal/pdf/pdf_file_parser.cpp
index e194aa82..83fc0660 100644
--- a/test/src/internal/pdf/pdf_file_parser.cpp
+++ b/test/src/internal/pdf/pdf_file_parser.cpp
@@ -19,7 +19,7 @@ TEST(FileParser, foo) {
       TestData::test_file_path("odr-public/pdf/style-various-1.pdf"));
 
   const auto in = file->stream();
-  const FileParser parser(*in);
+  FileParser parser(*in);
 
   parser.read_header();
   while (true) {
@@ -81,7 +81,7 @@ TEST(FileParser, bar) {
       TestData::test_file_path("odr-public/pdf/style-various-1.pdf"));
 
   const auto in = file->stream();
-  const FileParser parser(*in);
+  FileParser parser(*in);
 
   parser.read_header();
   parser.seek_start_xref();