Is it possible to add a watermark to a powerpoint and block it so it can't be erased

Hello! I'm new to VBA, specially Powerpoint's. I was wondering if it's possible to add from VBA an image watermark and block it so user's when seeing/editing the file can't modify or erase it?

Another solution would be converting the ppt to pdf with the watermark but, I want to consider this as the last option.

Is it possible?

I'm only somewhat familiar with Excel's VBA. And I found something but only works for text and doesn't say anything about blocking it. I'm assuming is somewhat similar.

It is possible to lock a watermark but since the XML has to be modified this is difficult via vba. Are you familiar with XML coding?

There is also an addIn to do this but it isn't free. I think the free trial may do it though.

ShapeLocker from OfficeOne

One problem may be that no block method will stop it being set to invisible with selection pane.