Are these local or online PDF files?
If local, does the same thing happen if you open Adobe Reader first, then open the file from there?
Does the pdf file show Adobe Reader's icon? right click on a pdf file, what's the first option?
Try this: Launch Reader, Go to Edit -> preferences, Click on general. You'll see a button called "Select Default PDF Handler" click on it. In the window that appears, select Adobe Reader XI and click Apply.Everything should work fine now.
I got there quickly as I was there several times. Yesterday after restarting my computer nothing has changed, but this morning I could chose between Adobe Reader XI and Adobe Reader and Adobe Manager Helper. And it works! Now I can say restarting my computer wasn't probably not enough. Thanks for your effort. I can say I learned a lot
Yes the pdf-files are local. Then the same happened.
Thank you for your reply. I appreciate it!
As you can see below, the problem has been solved.
there is no "Select Default PDF Handler" button