I would like to upload a PDF on my site. How can I do that?

Your first step is to check and see if the 'File Attachment' option is available on your content page.  It is located towards the bottom in between 'URL path settings' and 'Comment settings.'  If you do not see this option, email staff@bookweb.org, and ask to have the Upload module enabled. 

Then follow the instructions in the screenshot below: