When I did that before it would automatically open Acrobat, but after I installed Windows 8 and then 10, it opened Microsoft’s Reader app instead. when I get a PDF attachment in an email or from a link on a website.
And while I can just open Acrobat and then browse for the PDF file I want to read/work on, there are times when I just double-click on a PDF file to open it, e.g. I prefer to use Adobe Acrobat (or Adobe Reader if I’m on a computer where Acrobat isn’t installed) to read PDFs because I’m more familiar with it. The best example for me is Microsoft’s Reader app for reading PDF files.