An brief tip for every one who has the following

Problem

A document, opened out of a mail or an archive, can’t be edited in OpenOffice / LibreOffice. The tool just told you “Document is only opened for reading”

The solution

In the upper toolbar on the left side is a Button called “Edit file” – it should be the fifth if right – . This function removes the write protection and you can edit the document. The only thing you need to do after doing that: Save a new copy of the document.