I think your can use insert from URL, and use a file:// url.
Insert From URL supports http, https, httppost, httpspost, ftp, ftps, and file protocols.
So your saying that the url should look like the following:
(or in the case of temporary path)
Is that correct?
I tried this local and PSOS and am getting an error 1631 (connection failed) in both cases, with or without URL encoding
I don't understand why FileMaker didn't implement the insertPDF when running script(s) on the server.
I would bet that most people would want to save the PDF with the record, so this kind of makes the fact that you can do it on Server a moot point.
The syntax that works for me is "file:///Volumes" & Get(DesktopPath) & "[filname]"
I found it on this older post: Re: Insert From URL from local file: error 1631
Edit: Note there are 3 /// and the word Volumes in the file path. I agree that FileMaker could have made this easier!