How do I add an attachment to a page?
Is it possible to attach a PDF (or presentation or spreadsheet ...) file to a page?
First, upload the file by adding a "file" content item to a desired folder in your site.
Then, edit the page to which you wish to attach the file. Look at the bottom of the editing form for the Related Item(s) control. Use the Browse... button and find the file you just uploaded. Click on Insert to attach it to the page.