Hi Brian, thank you for reaching out. If you are looking to set up digital products to sell on your website, please review the following article with details instructions on how to do that: https://help.shopsettings.com/hc/en-us/articles/212590929-Digital-products 
If you are just looking to upload a pdf file and make it downloadable you can do this with the following steps:
1. Navigate to My Drive
2. Click on New-> File-> Upload from my Computer. Select the file and upload it.
3. Navigate to Modules
4. Drag the File Download module and drop it where you'd like it positioned.
5. Click on the button that you've just positioned and click on Choose file. This will take you to your Drive where you just double click on the PDF you want embedded into the button. Then Save and Publish  your website. 
If you need further assistance or information, feel free to reach out to us via live chat.