Poor Image Quality of Scanned Records Can They Be Improved Using Photoshop

I recently purchased 2 CD-ROMS of 1890 Union Veterans' Census records--Bradford Co., PA, and Ontario Co., NY. I was very disappointed in the poor resolution of the pdf images; most of them are nearly illegible. Apparently I neglected to read the fine print before buying--oh, well. However, I am determined to salvage something from the discs, and I figure Photoshop could be used to improve the image quality, but I have NO IDEA how to do it. It seems so easy on all the cop shows, doesn't it??? If any of you have any experience with this, I'd appreciate the help.--treenut