For PDFs I open that I want to keep I save into a folder somewhere else on the computer filed in an applicable folder.]]>
This article is about computer disposal but is also relevant to your question:
First, you should understand that deleting files, and even formatting your hard drive, are not sufficient. Both processes really just remove the information the hard drive needs to find the data, not the data itself. Deleted files can be undeleted and formatted hard drives can be recovered.
To be sure that your data is removed beyond all practical ability to recover it, you should use a wiping or erasing utility. These tools overwrite every sector of the hard drive with binary 1’s and 0’s. Those that meet government security standards even overwrite each sector multiple times for added protection.
Erasing Your Personal Data Before You Sell or Trash Your Hard Drive