Another PDF app was able to unlock PDF doc protected by password. Why?

[LouiseMSEI]

Hello,

I just realised that another PDF program can unlock a protected PDF.

The PDF document had a password preventing modifications, except printing.

Can you explain why the document was not really protected ?

Is there a way to make sure this cannot happen?

Thank you !

Louise

[Test Screen Name]

Many apps ignore editing password. It's a useful hint but no protection. Acrobat should have warned you of this but many people ignore the warning. 

[LouiseMSEI]

Thank you Test Screen Name. So, in other words, Acrobat doesn't really protect my documents even if I put in a password against modifications?

Is there another way to protect my documents? I want them to be opened, printed but not modified.

[Dave__M]

This has been an issue for years... and it's not anything Adobe can control when it comes to the behavior of a piece of software that is not produced by Adobe (as I understand it).  Many companies produce applications that open, view and manipulate PDFs.  How and whether the engineers honor the security parameters is their call, unfortunately.

My best,

Dave

[Dov Isaacs · Accepted solution]

To be a bit clearer about this.

The only password that provides strong protection is the password that you can set for opening the PDF file. That password is used to encrypt the PDF file such that if you don't have the password, a program reading the PDF file that doesn't have that password from the user cannot access the contenst of the file at all.

The ability to change the protections for modifications, printing, copying, etc. are controlled by a password, but that protection is only as good as the applications processing the PDF file. Adobe's PDF applications including Reader and Acrobat do obey those restrictions and won't let you change them without knowing the password. Regrettably, there are other applications that simply ignore the restrictions.

PDF is an ISO standard, not an Adobe standard and as such, we cannot control what mischief other vendors cause.

[Dave__M]

Thanks Dov!  I've had to answer questions regarding this very issue in the classroom for years.  

My best,

Dave

[LouiseMSEI]

Thank you, Dov Isaacs, for this clear answer!

Being in the the scientific field, it it important that our reports stay tamperproof.

I will look into other options.

I hope this will help others who think that their PDF is safe from modifications.

Have a very nice day !