After the recent update when I click on any PDF within Project Explorer it doesn't open Adobe anymore. If I close D-Tools and open the file outside of D-Tools then the PDF opens in Adobe.
You might have an issue with your Adobe install. This still works for me. Have you tried restarting Windows since the update?
@Kevin Frye: Yes and that didn't fix it, reinstalling Adobe does. This has happened before and is mentioned on the D-Tools Support Chat Ref 74165 from the 16th January 2019. I did get an error message so if it happens again I will screen shot the error message and send through.