FPDF_Creator can only create file through embedder-supplied callback.

core/src/fxcrt/fx_extension.cpp

Index: core/src/fxcrt/fx_extension.cpp
diff --git a/core/src/fxcrt/fx_extension.cpp b/core/src/fxcrt/fx_extension.cpp
index 0f610d271749f58ec6de0ae2971fe3a6e02319f1..d64a06d08b7fcc2dfc6f070037e73f76bb1aa7b4 100644
--- a/core/src/fxcrt/fx_extension.cpp
+++ b/core/src/fxcrt/fx_extension.cpp
@@ -36,12 +36,6 @@ IFX_FileStream* FX_CreateFileStream(const FX_WCHAR* filename,
   }
   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);
 }