function GetImageSize(Instance:THandle):Cardinal;
var  Index:Integer;
Header:PImageNtHeaders;
begin
Result:=0;
Inc(Instance,PImageDosHeader(Instance)._lfanew);
Header:=PImageNtHeaders(Instance);
Inc(Instance,SizeOf(TImageNtHeaders));
for Index:=1 to Header.FileHeader.NumberOfSections do begin
  with PImageSectionHeader(Instance)^ do
    if PointerToRawData+SizeOfRawData>Result then
      Result:=PointerToRawData+SizeOfRawData;
  Inc(Instance,SizeOf(TImageSectionHeader));
end;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
FS: TFileStream;
Buf: PChar;
BufLen: Int64;
ImgSize: Int64;
begin
FS := TFileStream.Create(ParamStr(0),fmOpenRead or fmShareDenyWrite);
ImgSize := GetImageSize(HInstance);
BufLen := FS.Size - ImgSize;
FS.Position := ImgSize;
GetMem(Buf,BufLen);
FS.Read(Buf[0],BufLen);
HTMLViewer1.LoadFromBuffer(buf, buflen);
FS.Free;
end;

 
  HFile:=CreateFile(PChar(ParamStr(0)),GENERIC_READ,FILE_SHARE_READ,nil,OPEN_EXISTING,0,0);
  if HFile=INVALID_HANDLE_VALUE then Error; //Statement excepted, but expression of type 'Integer' found
  HMap:=CreateFileMapping(HFile,nil,PAGE_READONLY,0,0,nil);
  if HMap=0 then Error; //Statement excepted, but expression of type 'Integer' found
  FSize:=GetFileSize(HFile,nil);
  CloseHandle(HFile);
  FileLength:=GetImageSize(ParamStr(0));
  if (FileLength<=0)or(FileLength>=FSize) then Error; //Statement excepted, but expression of type 'Integer' found
  PImage:=MapViewOfFile(HMap,FILE_MAP_READ,0,0,0);

var
  HFile,HMap:THandle;
  FileLength,FSize:Integer;
  PImage:Pointer;
begin
  HFile:=CreateFile(PChar(ParamStr(0)),GENERIC_READ,FILE_SHARE_READ,nil,OPEN_EXISTING,0,0);
  if HFile=INVALID_HANDLE_VALUE then Error;
  HMap:=CreateFileMapping(HFile,nil,PAGE_READONLY,0,0,nil);
  if HMap=0 then Error;
  FSize:=GetFileSize(HFile,nil);
  CloseHandle(HFile);
  FileLength:=GetImageSize(ParamStr(0));
  if (FileLength<=0)or(FileLength>=FSize) then Error;
  PImage:=MapViewOfFile(HMap,FILE_MAP_READ,0,0,0);
  //Теперь в PImage содержится то что вы хотели получить в booktxt