How do I upload/create a link to a document in a textbox?

You can upload a .pdf or document by linking to it in the textbox (much like creating a link to a website).
Select the down arrow in the textbox to open up the options.
Highlight the text in the textbox
Select the link icon in the text editor.
Browse to the file you want to use and select Open.
This will bring you back to the screen. Then select OK.
After saving your work, when someone clicks on the link they will be able to download and view the .pdf.