FPDF_Creator can only create file through embedder-supplied callback.

core/src/fxcrt/fx_extension.cpp

 // 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
 
 #include "../../include/fxcrt/fx_basic.h"
 #include "../../include/fxcrt/fx_ext.h"
 #include "extension.h"
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
@@ skipping 18 matching lines @@
   IFXCRT_FileAccess* pFA = FXCRT_FileAccess_Create();
   if (!pFA) {
     return NULL;
   }
   if (!pFA->Open(filename, dwModes)) {
     pFA->Release();
     return NULL;
   }
   return new CFX_CRTFileStream(pFA);
 }
-IFX_FileWrite* FX_CreateFileWrite(const FX_CHAR* filename) {
-  return FX_CreateFileStream(filename, FX_FILEMODE_Truncate);
-}
-IFX_FileWrite* FX_CreateFileWrite(const FX_WCHAR* filename) {
-  return FX_CreateFileStream(filename, FX_FILEMODE_Truncate);
-}
 IFX_FileRead* FX_CreateFileRead(const FX_CHAR* filename) {
   return FX_CreateFileStream(filename, FX_FILEMODE_ReadOnly);
 }
 IFX_FileRead* FX_CreateFileRead(const FX_WCHAR* filename) {
   return FX_CreateFileStream(filename, FX_FILEMODE_ReadOnly);
 }
 IFX_MemoryStream* FX_CreateMemoryStream(uint8_t* pBuffer,
                                         size_t dwSize,
                                         FX_BOOL bTakeOver) {
   return new CFX_MemoryStream(pBuffer, dwSize, bTakeOver);
@@ skipping 244 matching lines @@
 void FX_Random_GenerateCrypto(FX_DWORD* pBuffer, int32_t iCount) {
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
   FX_GenerateCryptoRandom(pBuffer, iCount);
 #else
   FX_Random_GenerateBase(pBuffer, iCount);
 #endif
 }
 #ifdef __cplusplus
 }
 #endif