Ok, I found out..
.. paid version do the same things as the free version, both let all apps read all files
.. the document protection from paid version.. is an automatic thing.. which scans all folders for pre-defined file types. And we can add some additional files ( not folders, and not file types ). But I was able to open such files with apps which are not whitelisted.
.. last but not least.. I was adding a pdf reader app to the blocked apps. And this app was still able to read protected files. But it was not able to change the file.
The ransomware protection seems to be working as intended. But the paid document protection ( which should protect documents with sensible data, such as bank data, passwords, IDs and so on ) is not working, because blacklisted apps can still open and read protected files.
Somehow curious