Detect if a PDF has a password

[hamelpierreluc]

Hello, I have some PDF with a password, so I can't open it with Adobe et see the PDF. But in .net code with PDFsharp, I can open the PDF and I don't see a properties to detect the password. This is a problem for us because we would detect the password and reject the PDF.

Do you know this kind of PDF? Do you have a hint for me ?

[packdat]

Have not tested it myself but a first naive approach that comes into mind is using an overload of PdfReader.Open that takes a PdfPasswordProvider as an argument.
When the password-provider is invoked, it means the library has detected that a password is needed to open the document and it uses the password-provider to ask you for the password.
You don't have to supply an actual password but you can use the fact that the provider was invoked to tell the PDF is password-protected.
Something like this:

var isPasswordProtected = false;
var document = PdfReader.Open(filePath, PdfDocumentOpenMode.Modify, passwordArgs =>
{
    passwordArgs.Abort = true;  // do not open the document
    isPasswordProtected = true;
});
if (isPasswordProtected)
{
    // discard the documemt
}

[hamelpierreluc]

The issue is that the PDF file opens without any problem using PdfReader.Open, but if I try to open it with Acrobat Reader or any other tool, a prompt appears asking for a password.

[TH-Soft]

Have you tried it with the PdfDocumentOpenMode.Modify flag?

[hamelpierreluc]

Sure :

var isPasswordProtected = false;
using var pdf = PdfReader.Open(fileStream, PdfDocumentOpenMode.Modify, passwordArgs =>
{
    passwordArgs.Abort = true;
    isPasswordProtected = true;
});
if (pdf.PageCount == 0)
{
    return false;
}

`

You have to know that it's not with all pdf with password, the majority of our pdf with password, pdfReader.Open goes in exception like we expect.