|Do they look poor when you view them on screen? Zoom it too to get more info.|
There are some pdf that may be scanned from older pages that are really images and not text. They may have been scanned bad.
You can get some programs to edit them if they are free to be edited.
You can sometimes set your grey scale settings for print or other contrast settings to correct for a few pages.
"The era of big government is over," said Clinton 1996