According to Adobe, there are more than 250 million PDF documents on the web today. The number will greatly increase since eBook and some portable devices become popular. PDF is really a good thing for reading and sharing. PDF have great reliability, almost anyone on any computer system can view PDF.
However, many PDF users are [...]

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 [...]