To use the Adobe Acrobat Pro (SUBSCRIPTION) software, you must have an active, paid subscription license to Adobe Acrobat DC. This can be purchased by an individual or provided by your company.
Once you have the subscription and you have clicked the link in your email to activate the subscription, you can launch the Acrobat Pro icon from the portal site and sign in to activate the software. Note that you will sign in using your Adobe credentials, not your Cloud credentials once Acrobat opens.
To change your default PDF handler, open the Remote File Explorer, find any PDF file, right-click the PDF file, select Open With, click Choose another app. Select Adobe Acrobat (not reader), check the box that says "always use this app", click OK.