Ask php how to determine if the pdf file is encrypted

Source: Internet
Author: User
How does php determine whether a pdf file is encrypted is a permission password, that is, it can be viewed and cannot be modified? I am working on a conversion program. if it is encrypted, it will be stuck there, if the problem persists, the project may be aborted ..., after encryption, there will be an encrypted sign. if you know the encryption principle, you can find the encryption sign to the language in which it is used. this is not a problem. how does php determine whether the pdf file is encrypted?
It is a permission password that can be viewed and cannot be modified.

I am working on a conversion program. if it is encrypted, it will be stuck there. if it is not solved, it may directly lead to a project abortion...

------ Solution --------------------
Encrypted, there will be a sign of encryption
If you know the encryption principle, you can find the encryption mark.
So what language is used is not a problem
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