Itextsharp Pdf，密码和水印保护

Question

Is there any function in Itextsharp whether pdf has password or watermark.

I have written below code but Contains("Downloaded By") will be dynamic every time.

byte[] bytes = Encoding.ASCII.GetBytes(FilePassword);
int page1;

if (FilePassword.Equals(""))
{
    PdfReader pdfReader = new PdfReader(CurrentPath, bytes);
    countWaterMarkFound = 0;
    // Calculate whether watermark exist in the pdf 
    for (page1 = 1; page1 <= pdfReader.NumberOfPages; page1++)
    {
        ITextExtractionStrategy strategy = new SimpleTextExtractionStrategy();
        string currentPageText = PdfTextExtractor.GetTextFromPage(pdfReader, page1, strategy);
        if (currentPageText.Contains("Downloaded By"))
        {
            countWaterMarkFound++;
            // adding new WaterMark here 
        }
    }
    pdfReader.Close();
}

Answer 1

Watermarks

A watermark is not necessarily marked as such in a PDF, you won't get a certain check for it.

Passwords

First of all, there are types of passwords in PDFs:

• the user password and
• the owner password .

If a PDF is encrypted and you open it with the owner password , you have full access to the PDF in PDF processors. If you merely open it with the user password , the PDF processor may limit your access according to the PDF specification.

There is a default password value given in the PDF specification. If a PDF is encrypted with that password as user password, you can usually open it without entering a password at all or entering the empty string as password.

If the user password is not the default password, you need to enter a password to open the PDF.

Thus,

• if you cannot open a PDF using new PdfReader(CurrentPath) , it is encrypted; in particular it is protected with a non-default user password (or a certificate);
• if you can open it using pdfReader = new PdfReader(CurrentPath) , check pdfReader.isEncrypted() ; if that returns true , the PDF is encrypted using the default user password; otherwise it is not encrypted.