How do I open a password protected PDF file?

Q: I wanted to know if there is any means to open a password protected
PDF file.

The class PDFDoc only takes one argument (the filepath). So, is there
any other class that can be used to open a password protected .pdf
A: To open secured PDF documents you can call InitStdSecurityHandler()
after creating the document:

For example:

PDFDoc doc = new PDFDoc("secured.pdf");
if (!doc.InitStdSecurityHandler("test")) {
  // Incorrect password ... try calling InitStdSecurityHandler() with
a different password?

For a full sample code please take a look at EncTest sample project

There some other ways to process secured PDFs using PDFNet but the
above approach is the simplest.