So you've got a bunch of files here and when you double click on them it automatically opens an app that handles that file. For instance, for these text files here if I double click it will open TextEdit. That's the default for these kinds of files. Now suppose you want to open it with something else. You can Control click to bring up the Context menu and then select Open With. Then you get a list here of all the different apps that handle this kind of file. Now some will allow you to edit it. For instance TextWrangler and BBEdit. Others will do different things like import it like some of these image editing apps here or maybe even a web browser that will just allow you to view it. But they'll all handle, in some way, that type of file. So I can open up with TextWrangler. It's a free text editing app that you can get in the Mac App Store. Now I can simply edit that file, this one time, using TextWrangler. But the next time I double click it will open it up in TextEdit. Now if I wanted to have that file opened all the time in a different app I can Control click on it to bring up the Context menu again but hold the Option key down and Open With changes to Always Open With. Now
how to change default pdf viewer macI can select TextWrangler. It will open it. It'll confirm and then now it opens in TextWrangler. But now when I close it and double click again you can see that file always opens with TextWrangler. However another file of the same kind like Test4.txt., that will still open in TextEdit. It's only this one file that has a flag set now to open in TextWrangler instead of TextEdit. I can change that back by Control clicking again, select Always Open With and select TextEdit, the default here, so that one now opens in TextEdit. I can also get information on here. So I can do File Get Info, or Command I, with that file selected. I've got an Open With section here. I can set that to be TextEdit, TextWrangler, BBEdit, anything I want. In addition I can hit this Change All button that appears here. Now all files that are that same type are going to now open with TextWrangler. So it tells you here, this change will apply to all documents with extension .txt. So I hit Continue and now when I double click on another text document it opens in TextWrangler. I can get info on that and you can see here it, indeed, is set to open with TextWrangler. I can set it back to TextEdit, Change All, and now they all once again will open in TextEdit.