Hi Loris,
you wrote
> $ file einladung.txt
> einladung.txt: news or mail, Unicode text, UTF-8 text
So you already have a simple textfile. Did you try the following?
enscript einladung.txt -o - | ps2pdf - einladung.pdf
Please note, "enscript" is a package which can easily be installed witrh apt.
Hope this helps.
Best
Hans