To add a document to your Project Dashboard, first you need to create the document, or upload it to Lumi.
See how to create a document.
See how to upload media.
To add a Document (word, excel, powerpoint, PDF) to your Dashboard:
Step 1: Find the item in Project Library
Press the three dots on the far right and "Add to Dashboard".
The pop up window will give you the option to "Show Header" or just add to Dashboard. You can choose whether or not to put a header on your item and choose a colour for the font and background.
Step 3: When you're finished, hit "Create