I wrote a mathematics textbook (high-school level), in PDF format. It is free and I just want it to be as widely-distributed as possible.
Converting it to any other format makes it awful. (It's merely awful when converted to .docx, but completely unusable when in .epub format.)
Many websites (e.g. Smashwords) don't accept PDF though. So I'm wondering if someone could give me a list of sites where I can publish my PDF ebook.
Scribd (https://www.scribd.com/1) will let you publish a pdf for free. If your original manuscript was written in latex you could also convert that to an epub, although that it can involve a little work.
Unglue.it is specially for free ebooks. And then there is the self-publishing platform of Gutenberg Project.
To add:
Both of the above are easy to use, support many formats, but require that your ebook be free.
Also, Library Genesis is not quite 100% legitimate.
Lulu is buggy and difficult to use. But your ebook doesn't need to be free. Also, it is the only close competitor to Smashwords (for US ebook publishers). They state:
PDFs sell wonderfully on the Lulu Marketplace!
But if you upload a PDF, it cannot be distributed to popular eBook channels such as Amazon Kindle, Apple iBookstore℠, Barnes & Noble NOOK™ bookstore, Kobo, and others.
If you'd like to distribute to these channels, Make an EPUB. We'll help you throughout this process, we promise.