Acrobat Pro DC Deactivation Hassle

How do I prevent Adobe Pro DC from being the default program to open my PDF files. I want the free version of Adobe Acrobat Reader to open my PDF files by default. I have a licensed copy of Adobe Pro DC which is licensed to be activated on two computers but only running on one computer. I am remote teaching and have a desktop running my remote learning station and I run a laptop to work on creating content at the same time. I need to open PDF files on both computers repeatedly to verify content. When ever I upgrade a computer Adobe Pro DC shuts down and has to be deactivated and reinstalled. Just replaced a CPU chip and none of my Adobe Pro products work on either computer. Also, I have to continuously shutdown Adobe Pro DC on one computer to open it on the other computer. I don't use Adobe Pro DC except to sign teaching contracts. It is completely unusable in a small working home office environment. 

Any ideas please. I can't afford to pay for two yearly licenses just so I can sign a couple of documents. Whoever in Adobe management who came up with this idea is losing the small home office market. Adobe products are top notch but licensing bites it big time. As soon as I get back to working in my school office (which has an institutional Adobe account), I'm going to discontinue my personal license and be thankful and good riddance to Adobe Pro DC.