Can you please describe what steps you are taking to view files? Generally, you have to download the PDF's from within the browser. Once downloaded, you can open the files and a dialog will appear asking you to choose which PDF viewer to use. Adobe Reader should be on that list if it's installed. Further, you can open Adobe Reader directly, go tot he Documents tab and browse your SD card to the Downloads directory to open the file.
I have the same problem, I think! I downloaded software but can't open the files in my HTC (android).. I got message somethink like File is Corrupted. But the same file I could open, than I am connected to my PC.