I have had Dell technical help trying for many days - they think it may have something to do with users and access? The documents are all the PDF documents that I have created by using PDF creator and/or cutePDF over the last several years. The only ones I can open are the ones that i have recently created. Two weeks ago I had to replace my hard drive and ever since I re-loaded PDF reader (i guess the new one..) it won't work for any of my older files. It is extremely frustrating to say the least. It is literally thousands of documents.
The same exact thing has happened to me, and I have been trying to figure it out for months! Please let me know if you find the problem!
May I know the application which you are using to open the PDF file? Also would you like to share any problematic PDF document so that we can test it?