PDF format becomes so popular because PDF has great security performance to protect the copyright. What’s more, PDF have great reliability that almost anyone on any computer system, for example, both Mac users or Windows users can view PDF files. No matter what language of your system is, you can view PDF. And you can [...]

Great security is one of the reasons why so many people use PDF format. A PDF author can set password to prevent readers from opening it, or set restriction for copying the text or printing the PDF document. They are the “User Password” and “Owner Password”.
But the security also bothers many PDF users. In [...]