Firstly, GIF is not a print image format so there seems little point in worrying about PPI definitions used in print graphics. I don't even think GIF supports PPI definitions.

If you select "save for web", Photoshop strips out your definition of PPI because it is irrelevant for GIF/PNG/JPG. When you reopen the file, Photoshop assigns an assumed PPI because it cannot find a defined PPI in the file's meta data.

There may be more to the story. Why is this an issue in your situation?

Hi Jim,

This is an image of a signature as a stamp.

The gif is attached as a stamp to the pdf (keeping transperancy) and we are trying to keep quality of the image.

We were doing this a month ago but some reason we lost the ability or the knowledge :D .

I think you would want TIF, not GIF, for defining both transparency and PPI.

The TIF format offers transparency (1-bit and 8-bit) and the ability to define PPI.

The GIF format only offers 1-bit transparency and no ability to define PPI.

Sorry, I skimmed over the part about this being in a PDF file. GIF would be more ideal for this purpose. While TIF supports transparency, Acrobat does not seem to want to place TIF in the signature stamp with transparency.

Your PPI is ignored when placing a graphic in a PDF file because Acrobat bases the size of the signature on the box you draw out in Acrobat, not the native resolution of the image file. So there is no reason to be bothering with PPI.