Scribd is a distribution service that lets its members download books from its library free of charge. It's one of the Draft2Digital services.
Today a stumbled across a PDF of one of my traditionally published titles on scribd that is not listed with D2D (it's hard copy only). I filed scribd's DMCA form and their response said this:
Content on Scribd is uploaded and maintained by our members and publishers with no editorial approval or other intervention by Scribd’s employees
Their members can upload anything they want and they make no effort to verify the members' rights to publish those titles.
You might want to see if they've got any of your books. Apparently you need to be a member to search their library. I found my book with a google search on my nephew's name. (He wasn't the uploader; we just have he same last name.) A search of my title and "scribd" went right to it.
https://www.scribd.com/document/70218236/C-Database-Development-1558283579
