Where can I find an instruction about FileMaker keeps its temporary folders and files?
Does that mean that you specify the temporary folder as the location where the PDF is to be saved when you use Save As PDF?
That is a standard folder specific to the OS. You can get the full file path for a given computer if you use Get ( TemporaryPath ) in 1) a calculation field, 2) a show custom dialog script step or 3) in FileMaker Advanced's Data viewer.
But numerous issues can be the cause of that error message. All it can really tell you is that FileMaker was unable to create a file with the specified name at the specified location. Lack of available space or folder "write access" permission settings are the least likely causes of this error messages. Invalid file paths, file names or possibly the presence of an open file with exactly the same name and location are much more likely issues to rule out first.