How to check if a PDF file is signed or not using iTextsharp in C#?

Question

I have a PDF file and I want to check whether it is signed by digital signature or not. using iTextsharp, the code in C#.

Answer 1

I would advise taking a look at the official examples.

They contain e.g. an example "SignatureInfo" which outputs multiple information items on all signatures embedded in a PDF; thus, they in particular determine whether a file is signed at all.

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It you are using iTextSharp 5.5.x, your pivotal code is this

public void InspectSignatures(String path) {
    Console.WriteLine(path);
    PdfReader reader = new PdfReader(path);
    AcroFields fields = reader.AcroFields;
    List<String> names = fields.GetSignatureNames();
    SignaturePermissions perms = null;
    foreach (String name in names) {
        Console.WriteLine("===== " + name + " =====");
        perms = InspectSignature(fields, name, perms);
    }
    Console.WriteLine();
}

(from the iTextSharp example C5_02_SignatureInfo.cs)

As you see, the method AcroFields.GetSignatureNames() gets you the names of all signed signature fields. If that list is non-empty, the PDF is signed.

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If you are using iText 7 for .Net, your pivotal code is this:

public virtual void InspectSignatures(String path)
{
    // System.out.println(path);
    PdfDocument pdfDoc = new PdfDocument(new PdfReader(path));
    PdfAcroForm form = PdfAcroForm.GetAcroForm(pdfDoc, false);
    SignaturePermissions perms = null;
    SignatureUtil signUtil = new SignatureUtil(pdfDoc);
    IList<String> names = signUtil.GetSignatureNames();
    foreach (String name in names)
    {
        System.Console.Out.WriteLine("===== " + name + " =====");
        perms = InspectSignature(pdfDoc, signUtil, form, name, perms);
    }
    System.Console.Out.WriteLine();
}

(from the iText 7 for .Net example C5_02_SignatureInfo.cs)

As you see, the method SignatureUtil.GetSignatureNames() gets you the names of all signed signature fields. If that list is non-empty, the PDF is signed.

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By the way, as you did not specify any further, I assume you mean regular integrated PDF signatures, in particular neither detached signatures nor XFA signatures.