iText7 C# Check PDF was locked after signature

问题

Hi i was trying too check if PDF file was locked after signature using iText7 .Net. Our current version was : 7.1.8

Currently i'm trying some piece off code but this doesn't respond to my research :

try
{
    //GET READER 
    PdfReader reader = new PdfReader(pdfModeleFile);
    if (reader != null)
    {
        //GET DOCUMENT 
        PdfDocument pdfDoc = new PdfDocument(reader);
        if (pdfDoc != null)
        {
            //GET FORM
            PdfAcroForm form = PdfAcroForm.GetAcroForm(pdfDoc, false);
            int signState = form.GetSignatureFlags();
            if (signState == 3)
            {
                //GET SIGNATURE
                SignatureUtil signatureUtil = new SignatureUtil(pdfDoc);
                List<string> signNamePdfAllField = signatureUtil.GetSignatureNames().ToList();
                List<string> signNamePdfBlankField = signatureUtil.GetBlankSignatureNames().ToList();
                SignaturePermissions perms = null;

                if ((signNamePdfAllField.Count() > 0 && signNamePdfBlankField.Count() == 0)){
                    //SIGNATURE WAS OK (ALL SIGNATURE WAS PUT)
                }
                else {
                    //ONE OR MORE SIGNATURE WAS MISING
                }
            }
            else
            {
                //SIGNATURE STATE OFF CURRENT PDF WAS NOT OK
            }
        }
        else
        {
            //PDF FILE HAVE NOT FORM
        }
    }
    else
    {
        //PDF FILE HAVE SOME PROBLEM
    }
}
catch (Exception e)
{
    //PDF FILE HAVE SOME PROBLEM
}

For explain i'm search solution to get this information (like on pdf adobe reader) :

Thank you in advance.

回答1:

Locking of the document after a signature is expressed by means of MDP (Modification Detection and Prevention) information of the signature. iText does not have explicit getters for these information but you can access them by using the generic, low level getters.

E.g. the following code prints the MDP information of the signatures of a PdfDocument pdfDocument:

SignatureUtil signatureUtil = new SignatureUtil(pdfDocument);
foreach (string name in signatureUtil.GetSignatureNames())
{
    Console.WriteLine("\nInspecting signature '{0}':", name);
    PdfDictionary dict = signatureUtil.GetSignatureDictionary(name);

    PdfArray referenceArray = dict.GetAsArray(PdfName.Reference);
    if (referenceArray == null | referenceArray.Size() == 0)
    {
        Console.WriteLine("The signature does not apply a transform.");
        continue;
    }

    foreach (PdfObject referenceArrayObject in referenceArray)
    {
        PdfObject referenceObject = referenceArrayObject;
        if (referenceObject.IsIndirectReference())
            referenceObject = ((PdfIndirectReference)referenceObject).GetRefersTo(true);
        if (referenceObject.IsIndirectReference())
        {
            Console.WriteLine("A transform is too deeply nested.");
            continue;
        }
        if (!referenceObject.IsDictionary())
        {
            Console.WriteLine("A transform is not a dictionary.");
            continue;
        }
        PdfDictionary reference = (PdfDictionary)referenceObject;

        PdfName method = reference.GetAsName(PdfName.TransformMethod);
        if (method == null)
        {
            Console.WriteLine("The signature does not provide the name of its transform method. (Invalid!)");
            continue;
        }
        if (new PdfName("UR").Equals(method))
        {
            Console.WriteLine("The signature is a usage rights signature.");
            continue;
        }
        if (PdfName.DocMDP.Equals(method))
        {
            Console.WriteLine("The signature has a DocMDP transform method, it is a certification signature.");
        }
        else if (PdfName.FieldMDP.Equals(method))
        {
            Console.WriteLine("The signature has a FieldMDP transform method.");
        }
        else
        {
            Console.WriteLine("The signature has the unknown '{0}' transform method. (Invalid!)", method);
            continue;
        }

        PdfDictionary transformParams = reference.GetAsDictionary(PdfName.TransformParams);
        if (transformParams == null)
        {
            Console.WriteLine("The transform has no parameters. (Invalid!)");
            continue;
        }

        PdfName action = transformParams.GetAsName(PdfName.Action);
        if (action != null)
        {
            if (PdfName.All.Equals(action))
            {
                Console.WriteLine("The transform locks all form fields.");
            }
            else
            {
                PdfArray fields = transformParams.GetAsArray(PdfName.Fields);
                if (PdfName.Include.Equals(action))
                {
                    if (fields == null)
                        Console.WriteLine("The transform locks all listed form fields but does not provide the list. (Invalid!)");
                    else
                        Console.WriteLine("The transform locks all the listed form fields: {0}", fields);
                }
                else if (PdfName.Exclude.Equals(action))
                {
                    if (fields == null)
                        Console.WriteLine("The transform locks all except listed form fields but does not provide the list. (Invalid!)");
                    else
                        Console.WriteLine("The transform locks all except the listed form fields: {0}", fields);
                }
                else
                {
                    Console.WriteLine("The transform uses the unknown action '{0}' for field locking. (Invalid!)", action);
                }
            }
        }

        PdfNumber p = transformParams.GetAsNumber(PdfName.P);
        if (p != null)
        {
            switch (p.IntValue())
            {
                case 1:
                    Console.WriteLine("The transform locks the document entirely.");
                    break;
                case 2:
                    Console.WriteLine("The transform restricts document manipulation to at most filling in forms, instantiating page templates, and signing.");
                    break;
                case 3:
                    Console.WriteLine("The transform restricts document manipulation to at most filling in forms, instantiating page templates, and signing, as well as annotation creation, deletion, and modification.");
                    break;
                default:
                    Console.WriteLine("The transform access permissions value is unknown: {0}. (Invalid!)", p.IntValue());
                    break;
            }
            Console.WriteLine("In a PAdES or PDF-2 context, addition of validation related information and proofs of existence is additionally allowed.");
        }
    }
}

You appear to be mostly interested in the "The transform locks the document entirely." output for the P value 1.

For backgrounds please study the PDF specifications ISO 32000-1 and ISO 32000-2 and the Adobe and ETSI extensions to it.

The Java equivalent can be found in the CheckMdpTransformations test testShowMdpForStep4SignedByAliceBobCarolAndDave.

来源：https://stackoverflow.com/questions/58397100/itext7-c-sharp-check-pdf-was-locked-after-signature