diff --git a/packages/fcl-pdf/src/fppdf.pp b/packages/fcl-pdf/src/fppdf.pp
index ce6d60ab03..c3126e113e 100644
--- a/packages/fcl-pdf/src/fppdf.pp
+++ b/packages/fcl-pdf/src/fppdf.pp
@@ -343,7 +343,7 @@ type
     procedure AddItem(const AValue: TPDFObject);
     // Add integers in S as TPDFInteger elements to the array
     Procedure AddIntArray(S : String);
-    procedure AddFreeFormArrayValues(S: string);
+    procedure AddFreeFormArrayValues(Const S: string);
   public
     constructor Create(Const ADocument : TPDFDocument); override;
     destructor Destroy; override;
@@ -842,7 +842,7 @@ type
     FTextMappingList: TTextMappingList;
     FSubsetFont: TStream;
     procedure   PrepareTextMapping;
-    procedure   SetFontFilename(AValue: string);
+    procedure   SetFontFilename(const AValue: string);
     procedure   GenerateSubsetFont;
   public
     constructor Create(ACollection: TCollection); override;
@@ -1104,9 +1104,9 @@ type
     function CreatePagesEntry(Parent: integer): integer;virtual;
     function CreatePageEntry(Parent, PageNum: integer): integer;virtual;
     function CreateOutlines: integer;virtual;
-    function CreateOutlineEntry(Parent, SectNo, PageNo: integer; ATitle: string): integer;virtual;
+    function CreateOutlineEntry(Parent, SectNo, PageNo: integer; const ATitle: string): integer;virtual;
     function LoadFont(AFont: TPDFFont): boolean;
-    procedure CreateStdFont(EmbeddedFontName: string; EmbeddedFontNum: integer);virtual;
+    procedure CreateStdFont(const EmbeddedFontName: string; EmbeddedFontNum: integer);virtual;
     procedure CreateTTFFont(const EmbeddedFontNum: integer);virtual;
     procedure CreateTTFDescendantFont(const EmbeddedFontNum: integer);virtual;
     procedure CreateTTFCIDSystemInfo;virtual;
@@ -1660,7 +1660,7 @@ begin
   end;
 end;
 
-procedure TPDFFont.SetFontFilename(AValue: string);
+procedure TPDFFont.SetFontFilename(const AValue: string);
 begin
   if FFontFilename = AValue then
     Exit;
@@ -3246,7 +3246,7 @@ end;
 function TPDFImages.AddFromFile(const AFileName: String; KeepImage: Boolean): Integer;
 
   {$IF NOT (FPC_FULLVERSION >= 30101)}
-  function FindReaderFromExtension(extension: String): TFPCustomImageReaderClass;
+  function FindReaderFromExtension(const extension: String): TFPCustomImageReaderClass;
   var
     s: string;
     r: integer;
@@ -3635,7 +3635,7 @@ begin
     AddItem(Document.CreateInteger(StrToInt(S)));
 end;
 
-procedure TPDFArray.AddFreeFormArrayValues(S: string);
+procedure TPDFArray.AddFreeFormArrayValues(const S: string);
 begin
   AddItem(TPDFFreeFormString.Create(nil, S));
 end;
@@ -5286,7 +5286,7 @@ begin
   Result:=GLobalXRefCount-1;
 end;
 
-function TPDFDocument.CreateOutlineEntry(Parent, SectNo, PageNo: integer; ATitle: string): integer;
+function TPDFDocument.CreateOutlineEntry(Parent, SectNo, PageNo: integer; const ATitle: string): integer;
 var
   ODict: TPDFDictionary;
   S: String;
@@ -5325,7 +5325,7 @@ begin
     end;
 end;
 
-procedure TPDFDocument.CreateStdFont(EmbeddedFontName: string; EmbeddedFontNum: integer);
+procedure TPDFDocument.CreateStdFont(const EmbeddedFontName: string; EmbeddedFontNum: integer);
 var
   FDict: TPDFDictionary;
   N: TPDFName;
diff --git a/packages/fcl-pdf/src/fppdfobjects.pp b/packages/fcl-pdf/src/fppdfobjects.pp
index 93de49dca0..4bc235ef46 100644
--- a/packages/fcl-pdf/src/fppdfobjects.pp
+++ b/packages/fcl-pdf/src/fppdfobjects.pp
@@ -166,7 +166,7 @@ Type
     class function ElementType : TPDFElementType; override;
 
     function GetDescription : String; override;
-    Function IsKeyword (aKeyWord : string) : Boolean;
+    Function IsKeyword (const aKeyWord : string) : Boolean;
     Function IsInteger : Boolean;
     Function IsInt64 : Boolean;
     Property TokenType : TPDFTokentype Read FTokenType;
@@ -328,7 +328,7 @@ Type
   Public
     class function ElementType : TPDFElementType; override;
     function GetDescription: String; override;
-    Function AddEntry(aKey : String; aValue : TPDFObject) : TPDFDictEntry;
+    Function AddEntry(const aKey : String; aValue : TPDFObject) : TPDFDictEntry;
     Function AddEntry(aEntry : TPDFDictEntry) : Integer;
     function ContainsKey(const aKeyword : RawByteString) : boolean;
     function IndexofKey(const aKeyword : RawByteString) : Integer;
@@ -395,9 +395,9 @@ Type
     Constructor Create(aSource : TPDFIndirect); overload; virtual;
     Destructor Destroy; override;
     Function ResolveObjectType : TPDFIndirect;
-    Class function FindClassForType(aType : String) : TPDFIndirectClass;
-    Class Procedure RegisterType(aType : String; aClass : TPDFIndirectClass);
-    Class Procedure UnRegisterType(aType : String);
+    Class function FindClassForType(const aType : String) : TPDFIndirectClass;
+    Class Procedure RegisterType(const aType : String; aClass : TPDFIndirectClass);
+    Class Procedure UnRegisterType(const aType : String);
     Class Procedure Register;
     Class Procedure UnRegister;
     class function ElementType : TPDFElementType; override;
@@ -463,8 +463,8 @@ Type
     Constructor Create; override; overload;
     Destructor Destroy; override;
     function FindResources: TPDFDictionary;
-    Function FindFontRefObj(aFontName : String) : TPDFRef;
-    Function FindFontRef(aFontName : String) : TPDFRefData;
+    Function FindFontRefObj(const aFontName : String) : TPDFRef;
+    Function FindFontRef(const aFontName : String) : TPDFRefData;
     Property ParentRef : TPDFRef Read GetParentRef;
     Property Parent : TPDFIndirect Read GetParent;
     Property Contents[aIndex : integer] : TPDFIndirect Read GetContent;
@@ -1785,7 +1785,7 @@ begin
   Result:=Fresources;
 end;
 
-function TPDFPageObject.FindFontRefObj(aFontName: String): TPDFRef;
+function TPDFPageObject.FindFontRefObj(const aFontName: String): TPDFRef;
 
 var
   aDict  : TPDFDictionary;
@@ -1802,7 +1802,7 @@ begin
     end;
 end;
 
-function TPDFPageObject.FindFontRef(aFontName: String): TPDFRefData;
+function TPDFPageObject.FindFontRef(const aFontName: String): TPDFRefData;
 
 var
   aRef : TPDFRef;
@@ -2604,7 +2604,7 @@ begin
   Result:='Value ('+Value+')';
 end;
 
-function TPDFValue.IsKeyword(aKeyWord: string): Boolean;
+function TPDFValue.IsKeyword(const aKeyWord: string): Boolean;
 begin
   Result:=(Value=aKeyWord)
 end;
@@ -2649,7 +2649,7 @@ begin
   Result:=Result+sLineBreak+'>>';
 end;
 
-function TPDFDictionary.AddEntry(aKey: String; aValue: TPDFObject): TPDFDictEntry;
+function TPDFDictionary.AddEntry(const aKey: String; aValue: TPDFObject): TPDFDictEntry;
 begin
   Result:=TPDFDictEntry.Create();
   if (aKey<>'') and (aKey[1]='/') then
@@ -3015,18 +3015,18 @@ begin
     end;
 end;
 
-class function TPDFIndirect.FindClassForType(aType: String): TPDFIndirectClass;
+class function TPDFIndirect.FindClassForType(const aType: String): TPDFIndirectClass;
 begin
   Result:=TPDFIndirectClass(_ClassList.Items[LowerCase(aType)]);
 end;
 
-class procedure TPDFIndirect.RegisterType(aType: String;
+class procedure TPDFIndirect.RegisterType(const aType: String;
   aClass: TPDFIndirectClass);
 begin
   _ClassList.Add(LowerCase(aType),aClass);
 end;
 
-class procedure TPDFIndirect.UnRegisterType(aType: String);
+class procedure TPDFIndirect.UnRegisterType(const aType: String);
 begin
   _ClassList.Delete(LowerCase(aType));
 end;
diff --git a/packages/fcl-pdf/src/fppdfparser.pp b/packages/fcl-pdf/src/fppdfparser.pp
index 00c380c4fa..d9852dc60e 100644
--- a/packages/fcl-pdf/src/fppdfparser.pp
+++ b/packages/fcl-pdf/src/fppdfparser.pp
@@ -88,7 +88,7 @@ Type
     Procedure DoWarning(Const Fmt : string; Const args : Array of const);
     Procedure DoError(const Nr : Integer; Const Msg : string);
     Procedure DoError(const Nr : Integer; Const Fmt : string; Const Args : Array of const);
-    Procedure DoUnknownStruct(aID : String);
+    Procedure DoUnknownStruct(const aID : String);
   Protected
     // Factory methods
     Function CreateScanner(aFile : TStream; aBufferSize : Cardinal) : TPDFScanner; virtual;
@@ -103,7 +103,7 @@ Type
     function VerifyDocument: Int64;
     // Stream Filters
     function FindStreamLength(aReposition : Int64): Integer;
-    function FilterStream(aStream: TStream; aFilterName: String;  aParams: TPDFDictionary): TStream;
+    function FilterStream(aStream: TStream; const aFilterName: String;  aParams: TPDFDictionary): TStream;
     function GetUnfilteredStream(aObj: TPDFIndirect): TStream;
     function ResolveFilters(aStream: TStream; aDict: TPDFDictionary): TStream;
     // XRef handling
@@ -380,7 +380,7 @@ end;
 Var
   aFileCount : Integer = 0;
 
-procedure SaveStreamToFile(aContext : String; aStream : TStream; const aFileName : String = '');
+procedure SaveStreamToFile(const aContext : String; aStream : TStream; const aFileName : String = '');
 
 Var
   FN : String;
@@ -1647,7 +1647,7 @@ Var
   aPredictor,aColors,aColumns,aBitsPerComponent : Integer;
   aStream : TPDFPredictStream;
 
-  Function MaybeInt(aKey : string; aDefault : integer) : Integer;
+  Function MaybeInt(aKey : string; const aDefault : integer) : Integer;
 
   begin
   if Data.ParamDict.ContainsKey(aKey) then
@@ -1697,7 +1697,7 @@ begin
 end;
 
 
-function TPDFParser.FilterStream(aStream : TStream; aFilterName : String; aParams : TPDFDictionary) : TStream;
+function TPDFParser.FilterStream(aStream : TStream; const aFilterName : String; aParams : TPDFDictionary) : TStream;
 
 Var
   Data : TPDFFilterData;
@@ -2110,7 +2110,7 @@ begin
   DoError(Nr,Format(Fmt,Args))
 end;
 
-procedure TPDFParser.DoUnknownStruct(aID: String);
+procedure TPDFParser.DoUnknownStruct(const aID: String);
 begin
   DoError(penUnknownConstruct,SErrUnknownConstruct,[aID]);
 end;
diff --git a/packages/fcl-pdf/src/fpttfencodings.pp b/packages/fcl-pdf/src/fpttfencodings.pp
index 4d9b35a657..7b41f9985d 100644
--- a/packages/fcl-pdf/src/fpttfencodings.pp
+++ b/packages/fcl-pdf/src/fpttfencodings.pp
@@ -34,11 +34,11 @@ Type
   PTTFEncodingValues = ^TTTFEncodingValues;
 
 Procedure GetEncodingTables(E : TTTFEncoding; Out ANames: PTTFEncodingNames; Out AValues: PTTFEncodingValues);
-Function GetEncoding(AName : String) : TTTFEncoding;
+Function GetEncoding(const AName : String) : TTTFEncoding;
 
 Implementation
 
-Function GetEncoding(AName : String) : TTTFEncoding;
+Function GetEncoding(const AName : String) : TTTFEncoding;
 
 Var
   Names : Array[TTTFEncoding] of string =