All the suggestions thus far sound good. Good PC housekeeping could be to run scandisk and defrag your hard drive. If you need further help please ask. What are your PC's specifications, processor speed, amount of ram and how many chips.
It could be your system simply lacks enough processing power for the task of opening the pdf documents in AR 6. It may be that you have a faulty segment on one of your ram chips. It may be simply that installing another stick of ram to boost your system would solve your processing problem.
When looking a the tasks in W98, if it appears the task is not responding it may just need more time to process. As per previous advice from other posters close all other apps while you try and open the pdf documents.
