What is a sealed envelope?
Some universities want you to send your certificates in a sealed envelope by post or bring them with you when you arrive.
Some evaluation companies also require a so-called sealed envelope.
To do this, you have your school or university put the certificates in an envelope, seal it and stamp it on the adhesive surface.
It could look like this, for example:
As a rule, you only need to put the native-language certificates in the envelope, you don't need the translations at most universities, they are urgently needed for the evaluation, but then you simply enclose them. Incidentally, WES for example insists that the adhesive surface is NOT sealed again with adhesive tape, as this makes it look as if the envelope has been opened again!