Which systemic prerequisites are necessary?

A browser of your choice is required to read the Messenger messages.

If you receive a PDF file as an attachment in Messenger, you should always read it with Acrobat Reader. Acrobat Reader can be downloaded free of charge from https://acrobat.adobe.com/de/de/acrobat/pdf-reader.html.

Here you see an example message in your inbox: To read it, please click on it.

This window will then open. Here you have the possibility to export the e-mail into different formats.

Why might that be necessary?

e.g. to open and/or save the message in your Outlook.

The other options like PDF or PDF (encrypted with user password) is also used to secure your emails.

Printing the e-mail is of course also possible for filing for your records.