Hi Wendy
We can confirm that the behaviour of prompting a user to enter a password when using an editor is intentional.
Set document protection
* Remark: the protection against modification is for people who have the full Acrobat product.
* If you don't set any password, the document will open as usual. If you set a user password, the PDF viewer will ask for it before displaying the document. The master password, if different from the user one, can be used to get full access.
This is from the SetProtection method description and is to ensure certificates are not being changed by users after being issued. Unfortunately there is no option in the user interface to switch this off. By default Totara does not set a password and this is why it's possible to access without one.
The code that controls/enables this in the standard Totara certificate module is:
$pdf->SetProtection(array('modify'));
We've not tested this but removing this/commenting it out from this from each of the four certificate types should remove the password protection (i.e */mod/certificate/type/XXX/certificate.php*). You should _not_ need to edit the tcpdf library at all ( lib/tcpdf/tcpdf.php).
Changes of this type would be considered a customisation and would need to be fully tested by yourselves (any issues that were a result of customisation would be unsupported).
Regards