FPDF_Creator can only create file through embedder-supplied callback.

core/include/fxcrt/fx_basic.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef CORE_INCLUDE_FXCRT_FX_BASIC_H_
 #define CORE_INCLUDE_FXCRT_FX_BASIC_H_
 
 #include "fx_memory.h"
@@ skipping 146 matching lines @@
 
   FX_STRSIZE m_Length;
 };
 
 class CFX_FileBufferArchive : public IFX_BufferArchive {
  public:
   CFX_FileBufferArchive(FX_STRSIZE size = 32768);
   ~CFX_FileBufferArchive() override;
 
   void Clear() override;
-
   FX_BOOL AttachFile(IFX_StreamWrite* pFile, FX_BOOL bTakeover = FALSE);
 
-  FX_BOOL AttachFile(const FX_WCHAR* filename);
-
-  FX_BOOL AttachFile(const FX_CHAR* filename);
-
  private:
   FX_BOOL DoWork(const void* pBuf, size_t size) override;
 
   IFX_StreamWrite* m_pFile;
-
   FX_BOOL m_bTakeover;
 };
 
 struct CFX_CharMap {
   static CFX_CharMap* GetDefaultMapper(int32_t codepage = 0);
 
   CFX_WideString (*m_GetWideString)(CFX_CharMap* pMap,
                                     const CFX_ByteString& bstr);
 
   CFX_ByteString (*m_GetByteString)(CFX_CharMap* pMap,
@@ skipping 1088 matching lines @@
   FX_FLOAT c;
   FX_FLOAT d;
   FX_FLOAT e;
   FX_FLOAT f;
   FX_FLOAT g;
   FX_FLOAT h;
   FX_FLOAT i;
 };
 
 #endif  // CORE_INCLUDE_FXCRT_FX_BASIC_H_