I ended up with a problem while I was away. I did not take my laptop, only my 1 GB USB Drive loaded with portable versions of Firefox, Thunderbird and OpenOffice.org.
The problem was that the computers available in the business center wher I was staying did not have Adobe Reader, in any version, installed. I was therefore unable to open any PDF files.
I went looking around and found Foxit Reader 2.0 for Windows from Foxit Software http://www.foxitsoftware.com/pdf/reader_2/down_reader.htm.
I downloaded it to my USB drive, double clicked on the FoxitReader.exe file and was able to access PDF files to my heart’s content and even fill in interactive forms, without having to install anything. On top of that it is much faster loading than Adobe Reader, in my experience.
Note: The paid version with enhanced capabilities does have an installer and writes to the registry, at least that is my understanding.
The free version does not have all the capabilities of Adobe Reader, but for the price and my uses, it is very adequate. I must say that I also have the full Adobe Acrobat 7 application on my main computer, with which I can generate PDFs and manipulate them, as well as just read or fill in interactive PDFs.
If I keep having no problems opening and reading PDF files in the next few weeks, Foxit Reader will become my default PDF reader.
Give this a try and you might be using it as your default PDF reader as well.