Product description fields are fully HTML formattable so if you are working in HTML, then you can use code to link to a pdf that is hosted on your server.
For those who don't know HTML or prefer not to code, using the built-in WYSIWYG editor will allow the same functionality. Here's what you need to know:
1. Your pdf file must be hosted on your own server, and you need to know the URL for the file (http://yourfile’saddresshere.pdf)
2. In your Nexternal Order Management System (OMS) Go to Settings / Boolean Options (bottom of the Setting Section). Click Edit. Be sure your WYSIWYG Editor is activated. At the bottom of the page, click “Next” to save.
3. Go to Products and find the product you want to edit. Click on the blue edit pencil.
4. In the Long Description (or any other WYSIWYG field) type in the text you want to use for the hyperlink.
5. Highlight the text with your cursor, and click on the blue globe with the chain links (as shown with arrow). (the blue globe can be in a different position, depending upon your browser and operating system) Then a popup window will appear. In the popup window, enter the URL where your pdf file is being hosted. Click ok.
Note: If you want the pdf to show up in the same tab of the browser in which a person clicked the download link, then leave Target: at ”__self”. If you want the pdf to open in a separate tab (recommended), then for Target, select “__blank”.