What to Do When Your Mac Can’t Open a File
If you try to open a file, but OS X El Capitan can’t find a program to open that file, OS X prompts you with an alert window. The figure shows what happens when you try to open a very old (1993) file created on a long-defunct Psion Series 3 handheld PDA (a file so old that most of you have probably never seen the .wrd file extension).
Click Cancel to abort the attempt to open the file, or click the Choose Application or Search App Store button to select another application to open this file.
If you click the Choose Application button, a dialog appears (conveniently opened to your Applications folder). Applications that OS X doesn’t think can be used to open the file are dimmed. For a wider choice of applications, choose All Applications (instead of Recommended Applications) from the Enable pop-up menu.
You can’t open every file with every program. If you try to open an MP3 (audio) file with Microsoft Excel (a spreadsheet), for example, it just won’t work; you get an error message or a screen full of gibberish. Sometimes, you just have to keep trying until you find the right program; at other times, you don’t have a program that can open the file.
When in doubt, use a search engine to read about the file extension. You’ll usually find out more than you need to know about what application(s) create files with that extension.