I have some PDF files that I want to open in preview, and others that I want to open in Acrobat. It would be nice if I could just set up that acrobat files with a different extention, say ".apdf" and have the mac automatically open anything with .apdf with acrobat, and anything with .pdf with preview.

But that doesn't seem to work, because I think that the filetype is actually part of the file, not just the filename...

any ideas?

  • You could probably make a simple Automator app which opens the file in either PDF app, based on its tags (defaulting to one of the apps of course). Then set all PDFs to be opened with your new app...
    – D.G.
    Jan 11, 2017 at 13:31
  • (That would be a solution for "the larger issue you're trying to solve" not "the question you asked" if it wasn't obvious.)
    – D.G.
    Jan 11, 2017 at 14:06

2 Answers 2


Select the file in Finder, then get info (cmd-i), and change the file extension (under name and extension) to something that is not used by other files.

Then, near the bottom of the get info window click "Open With" and select the app you need, i.e. Adobe Acrobat, by browsing through your application list. Then, at the bottom of that sub-pane click the 'change all' button. This will direct Acrobat to open all files with the extension you chose.

  • 1
    Useful information on the Open with... function, but it doesn't actually answer how the OP can differentiate files by this method.
    – Tetsujin
    Jan 10, 2017 at 7:44
  • When I did the "change all" button, it tried to change all PDF files, because it still knew that it was a PDF file, even thought it had the type PDF... Jan 10, 2017 at 22:12
  • I tested this with your example, changing a x.pdf file to an x.apdf extention, and mapping this as I described to adobe reader. The x.apdf file is opened by Acrobat, while other pdfs are still opened by Preview. PDFs do have info in the header, but at least on my system (10.10.2) it works as above.
    – Dennis
    Jan 12, 2017 at 0:45
  • @tetsujin-- the differentiation is in the unique file extension. .pdf versus .apdf
    – Dennis
    Jan 12, 2017 at 0:47
  • I'm not sure why this didn't work initially... but yay! ALso, annoying that acrobat won't save with anything other than the pdf extension... so I have to save, and then change manually... but oh well... Jan 18, 2017 at 16:15

While renaming a file on the desktop usually doesn't change its extension (filetype) even if you try to, you can change the name and extension in the Get Info screen. Just two-finger click (or right-click) on any file, hit Get Info, and type in any name and extension you want in the Name and Extension field of the window that appears.

Problem solved.

tl;dr: Get Info the file and change its filetype there.

  • But I need to do this for every document... which doesn't solve the problem in the large... Jan 10, 2017 at 22:13

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .