There are multiple ways to do this. You must have the PDF saved on your computer to do this.
1. Click on the reference you want to add the PDF to and click on the paper clip button from the reference/preview panel (typically on the right of the screen). Navigate to where the PDF is saved.
2. Click on the reference you want to add the PDF to and go to the References menu and select File Attachments-> Attach File. Navigate to where the PDF is saved.
3. Double click on the reference to open it in the edit mode. Click and drag the PDF file into the reference. It does not matter where you drag it, it will go into the File Attachments field.
You must save the reference after attaching the PDF. You can go to the File menu and select Save or if you have the reference open in edit mode, you can close the edit reference window (not the entire program) and it will ask if you want to save it.
