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?
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.
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.
