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Jul 11, 2018 - Back in the pre-Mac OS X and macOS days, Apple's System 9 and earlier relied on hidden metadata to associate files with apps.

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Change the Default by Using Open With in File Explorer Open File Explorer and navigate to a folder containing your PDF file. Right-click on a file and choose “Open with > Choose another app”. A pop-up will appear that will let you choose a program for just one time. Or you can also select the “Always use this app” link to make it permanent. From this window, choose the default PDF reader of your choice. If the default app is not listed in this window, then you can select a different program located in your PC. Click “More apps”, select an app or scroll down to see “Look for another app in this PC” link.

Click this link to browse to the program that you want to set as the default PDF reader, and choose the “Open” button to set it as the default. Change the Default by Using Default Programs in Control Panel Open Control Panel (icon view) and select “Default Programs”. Click the link labelled “Associate a file type or protocol with a program”, and wait for a couple of seconds to load all file types. Scroll down the list to see.PDF entry.

Click on “.PDF” entry, and then click the “Change program” button. A pop-up will appear that will let you choose an app from the list.

If the default app is not listed in this window, then you can select a different program located in your PC. Click “More apps”, and select an app or scroll down to see “Look for another app in this PC” link. Click this link to browse to the program that you want to set as the default PDF reader, and choose the “Open” button to set it as the default. Changing the default PDF reader app in Windows is a simple procedure, and that’s all there is to it.