Summarize the following:
It's usually at the bottom-left corner of the screen. It's on the left side of the menu.  It's in the left column. A list of file types will appear along the left side of the window, with each associated app on the right. ” The current default viewer appears to the right of this entry. For example, if it's currently set to Google Chrome, click Google Chrome. A list of apps that can read PDFs will appear. The selected app will now open PDFs on your PC by default.

Summary:
Click the  menu. Click . Click Apps. Click Default apps. Scroll down and click Choose default apps by file type. Scroll down to “.pdf. Click the default PDF reader. Click the app you want to use.