Password Protect Folder of PDFs

Good Afternoon All

Scenario:
I've been approached by a department in regards to creating a solution for a monthly invoicing process. At the moment they manually send out each email with a copy/paste message and attach a PDF that they have already manually added a password to. I've managed to address automating the emails and attaching the PDFs, but I've been asked if there is any way of automating the final step. The current process dumps around 300 PDFs into a folder which is where they are picked up and manually adjusted.

Is there any way within VBA to apply a Password to all the files within a set folder?
We have reference data so that each file could be identified and given a separate password.

I'm just struggling as some sites are saying it can be done but aren't clear, others say it is impossible without a 3rd party plugin. I doubt the company I work for will allow the 3rd party plugin, however that only appears to be for exporting the files from source, not updating existing PDFs.

Any help would be greatly appreciated.

Many Thanks, Chris