The Dutch postal company offers a service that will let companies send physical letters by uploading pdf files. The uploaded file is printed, folded and put into an envelope and sent to the destination.
Our product (Moves) supports this by allowing planners to send letters to their clients with no hassle at all. If you'd like to use this too, you can use our open-source plugin TNTService. You can find it on Github here.
Although the plugin is free you will have to pay for the service ;) You can get a subscription here.