You're at your computer printing out thirty party invitations when you discover you only have 3 envelopes. What to do?
Run those invites through the printer again and print a design from Letterfu on the back. Five folds and a tuck turns the invitation into its own envelope, sealed with the postage stamp. There are 4 designs available on the Letterfu website, links to several other folks' designs, and all the tools you'll need to create your own vector designs.
So, when's the party?
