To post a .pdf you can either use your

1. control panel or
2. the FTP client.

Your files on the server are similar to files on a desktop.

From FTP: Under httpdocs I would create a file called downloads- or something similar. Then when you upload the document onto the server, in that folder the link will be yourdomain.com/downloads/filename.pdf

To upload a file within Wordpress: from your dashboard go to "Media" and "Add New". Locate the file and upload. Before saving the filepath will be listed right above the save/upload button. Highlight and copy this filepath.

Within your WordPress Dashboard, go to Pages and create a new page, or edit an existing one (or edit a Post for that matter). Within the page, type what you would like the visitor to click on to download the document (example: "Download my Price List") - or include an image. Then add a hyperlink (paste the filepath name from the file you've just uploaded) to the document for download.