STEP 1: Click the start button:
STEP 2: Start typing "default programs" and click the icon with the gear as shown below:
STEP 3: Select "Set defaults by app" as circled below. You may have to scroll down on the page to get to the bottom:
STEP 4: The following window will appear, select Adobe Acrobat DC and the choose "set this program as default" as highlighted in yellow below. Do not choose Acrobat Reader (Make sure you choose the exact program as shown below):
Click "OK" and PDF files will now open in Acrobat DC Pro.