How do I add a PDF to an existing record in a folder?

PROBLEM:
How do I add a PDF to an existing record in a folder? In other words, let's say that I do a search and then get the PDF on a later date. How do I link the PDF to the record in the folder?

SOLUTION:
There are 2 options available:

1. If PDF stored on local/ shared drive:
a. right click on the article
b. select "Associate with a File"

2. If the initial search was done on PubMed channel:
a. right click on the article
b. select "Retrieve PDFs for selected article(s)"