To add a link to a file follow the basic steps.

1. Add new post or open an existing.

2. Place cursor where you would like the link to appear.
3. Click "Add Media" button.
4. Using the file selection option, select your PDF and click the upload button.
5. After it uploads, you'll have this new section that shows a Title, Caption, Description, and Link URL. 

6. Place the link text you want to appear in the post into the Title field.
7. Click "File URL".
8. Click "Insert into Post".

9. Place the cursor somewhere within the newly created link.

10. Click 'Insert/edit link' on the toolbar.

11. Select 'Open link in a new tab' and click Update.