Canva strips security from any permissions locked PDF file - any solution??

This is also posted within the Acrobat section, but is also relevant to designers within inDesign.

Background:

We supply PDF files to our client (export from inDesign). On occasion, they like to make their own amends to these using Canva. The problems are obvious - our projects get re-appropriated for other use, the quality of the images, colours, and design is lost (images become mush, typographic formating lost), and we lose control of the editable master copy (artwork) - so whenever we have to make amends which the client cannot, we have to trawl through their Canva edited file to find the amends they have made and apply them. Furthermore, the Canva version looks terrible which makes our work look bad - a business risk.

The problem:

I thought that providing the pdf with all editing prohibited - no changes, no copying of text / images / no access for screen readers etc - all denied would fix this problem. However, when we tested this - bringing in this locked pdf into Canva it becomes fully editable.

Solution?

Apart from this being a massive security issue - where seemingly any copy within a locked pdf can be freely changed, is there another solution where the file can be locked down? Canva will not import a password protected pdf, however that is not a solution as the files we supply need to be distributed.

Many thanks for help.