Find yourself a folder from somewhere. Preferably with beautiful or funny images inside.
Once you've chosen, look inside to find good spots to "write on". At tgis picture it would look great to write inside the box, with scissors around it, and underneath the picture to the left.
Cut out white paper, that match the spots you've chosen.
Glue the paper on the spots you've chosen througout the entire folder.
Write your letter.