I recently backed up my home computer, reinstalled Ubuntu Linux and decided the terabyte-sized external hard drive was a must. (I recall my younger self backing up with floppy disks. A quick calculation suggests it would take 7510 pounds of those old disks for my current data. And I'm nowhere close to using up that terabyte.) So I've taken all my CD and DVD backups and am making one grand version of my data. This will take a while to clean up.
Among those files, I have collected more than 4,000 unique PDFs. Surely some are of use to my reader, so as I review them, I will post them if they're in the public domain, or point to where you can download them if not.