If you wish to add a Document Link to an Application form, you must either use the Attachments page and adjust the Text OR use a Text: Notes field to include the necessary HTML code you will need to add a hyperlink.
The code to create a hyperlink is as follows (without quotations):
"<A HREF="https://www.myfoundationsiteurl.com/mydocument.pdf">Click here to download the document</A>"
The A HREF points to the web address of your document. Between the brackets is the text that will be clickable by your applicant that leads them to that document; in the above example, the linked text would read as "Click here to download the document".
Further references to HTML coding and how this works may also be found at https://www.w3schools.com/html/