If you have a file that opens with a program and you wish to change the program it's using, you can change the default application for that type of file. 

For example, if you have a PDF that is opening with your Internet browser, but you want it to open with Adobe Reader, follow these steps:

Click in the search bar or click the Start icon and begin typing "default" and you will see Default apps appear:

Click Default apps to launch this settings screen.

Choose your default apps for the programs listed, or scroll down and select Choose default apps by file type.

For Adobe PDF's, scroll down to the .PDF file type and click to change it to your desired application. Recommended choices are Adobe Reader or Adobe Acrobat.

Once you have made your selection, you can close the Settings window.

Another method is to right-click the file you wish to open and choose "Open with..." and a window will appear. Click More apps to see the full list of applications. Check the "Always use this app" option, and then click your desired application:

NOTE: This is a per-user setting, meaning if numerous persons login to the same PC, each user will need to specify their own settings.