absolute file path on Windows

Hello, I have a postscript program which needs to output some text to a file. I declare the filename like so:

/tmpfile (input.mrd) (w) file def

Currently, it outputs to that file name in the same directory that I run the postscript program. I need it to output to a different directory, outside of where I am running the program. For example, I might want to output to "C:\Myfolder\input.mrd".

I have tried several different ways of declaring the file, such as
/tmpfile (C:\Myfolder\input.mrd) (w) file def, or
/tmpfile (C:/Myfolder/input.mrd) (w) file def, or
/tmpfile (Myfolder\input.mrd) (w) file def, or
/tmpfile (C:\\Myfolder\\input.mrd) (w) file def.. etc.

but none of those work. Any help would be greatly appreciated. Thank you.