To add a PDF to a page you first need to upload it, please see: How to Upload a File
Now you will need to access the page that you are creating.
Go to: CONTENT >> EDIT WEB PAGES
Click Edit on the page:
You can add the PDF link to text, to an image or both.
Highlight the text area and Click on Insert Link.
Add the path to your PDF, it is just the relative part of the URL like this: /images/pdf.pdf
Click on the image, and follow the same steps.
Click on Save Web Page:
Lastly, Click on View Page: