How to make a url based on Username?

[yotsume]

QUESTION: How can I code a link to an external file such as a pdf where the member's username becomes part of the url so each link is unique to that user based on who is logged in. So when a user clicks the link they can download their file based on their username. When a different member is logged in they are taken to their file because the url will reflect their username instead...

Example: www.mydomain.com/files/username.pdf

So the username portion of the url would be pulled from vbulletin.