For work you need:
- A4 paper
- double sided tape
Print one of the templates of envelopes below on your printer.
Cut it out with scissors and bend at marked lines.
Sttick the folds together with the double sided tape.
Here's the envelope. There are white boxes for stamps and signatures on the envelope.
I hope that my DIY will be useful for you.
I'm always happy to share with you what I can do.