There is something I was able to do with Gimp 2.8 and not with the 2.10.8 version. In order to use some stamps in pdfs, I have to create them from scanned documents, possibly where they appear on a white background. What I do is crop the scanned document to the stamp, apply the commend "color to alpha", then export to pdf to obtain a stamp that can be used on various pdf software with the proper function.
The problem is that with the 2.10.8 version of Gimp, the exported pdf does not retain the transparent background. The same procedure works fine with the 2.8 version.
Any clue? Thanks!