Here is an update on this. The team made a proof of concept with Nextcloud integration. You can find the repository here. You will still need to manually install the App. The instructions are in the repository. It has been tested with versions up to Nextcloud 17.
The functionality is still incomplete and currently only allows you to register a document and obtain a receipt via the Peercoin blockchain. In case you wonder what WIF is, it stand for wallet import format. It is basically the private key from your wallet. Please handle with care as it also provides access to any coins you hold on this address.
Edit: Current version uses testnet, so only private keys from testnet will work
Find the Perpera functionality added into the details of each document. (see also screenshot below)
We are still working on integrating key management with Perpera and simplifying and completing the user interface to cover all required functions and setting up a demo with free testnet coins.
In the mean time please let the team know what you think, what your use case would be and whether you would use it.