Add Digital Signature to Documents in a Document Library using C#

Freddy Mounir

Digital Signatureadd digital signatures to documentsDocument Digital Signatureord documents

10 Comments

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Barath13y ago
Can you please share the code?
Pooja14y ago
Hi, Can ypu plz share the source code for the above article as i have the same requirement and need it urgently. Thanks in advance
hr hrs14y ago
when exec this code wordDocument = wordapp.Documents.Open variable (wordDocument) is null ??? my file is exist
Praveen Kumar17y ago
I just found another one which exists like a feature and which is using docuSign signature as the digital signature here on codeplex. http://esignspdocuments.codeplex.com/
- Freddy Mounir17y ago
  thnx dear , but my component also can be installed as a feature , and i will upload the source code so you can install it , within 2 days regards; Freddy Khalaf
Chinh Tran17y ago
THanks
- Freddy Mounir17y ago
  Welcomed dear
ds ps17y ago
do u have the demo project for this? if so, can u share it? actually i also have to develop the program for document management where documents are signed by authorised levels i.e one after another(predefined persons/authorities). and that document should be approved/signed respectively... but have no idea how to do it... plz share any related topics/ demo projects .. thanks
- Freddy Mounir17y ago
  dear ; thanks for having interest in this article , and about the source code , the project it self i will upload it soon , but it may take from 2 or 3 days , but dont worry i will upload it for sure Cheers; Freddy Khalaf
- Freddy Mounir17y ago
  dear; ive uploaded the source code you can now download and work with it , and sorry for delay , and to know how to install it please go to : http://sptechytalks.blogspot.com

I had a requirement that involved adding a digital signature to word documents uploaded on a document library when the document is approved. This article discusses step by step how to add digital signatures to word documents.

I solve this problem by using the following approach.

Step 1
Catch the update events (by writing ItemUpdated event handlers) (for more info about event handlers implementation see the previous post).

Step 2
Make a copy of your file that is approved in the document library to a temporary folder on the server.

Step 3
Add the digital signature to your own copied file on the server.

Step 4
Write the file again to your document library then remove the temporary copy on the server.

Step 5
If the file is not signed the approval status of the document will be converted into rejected.

I have used the following code to implement this entire process.

The Strings Class is a class that contains all strings used in my code. Listing 1 shows the Strings class and its members.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace DGEventReciever

{

public class Strings

{

// The general keys .

#region

public const string TemporaryFolderKey = @"C:\TempFolder";

public const string ApprovalColumnKey = "Approval Status";

#endregion

//Other Strings.

#region

public const string InDraftStatus = "0";

public const string DateFormat = "yyyyyMMddhhmmss";

public const string IDColumn = "ID";

public const string NameColumn = "Name";

public const string DocxExtension = ".docx";

public const string DocExtension = ".doc";

#endregion

}
}

The Main Class that handles the events is listed in Listing 2. I have used OfficeInterop COM library. Before you use this code, you must add reference to Microsoft.Office.Interop.Word.Dll and other required assemblies.

using System.Web;

using Microsoft.SharePoint;

using System.IO;

using Microsoft.Office.Core;

namespace DGEventReciever

{

public class DGEventHandler:SPItemEventReceiver

{

//All the Public Used Variables.

#region

public string TemporaryFolder = string.Empty;

public string ApprovalColumnName = string.Empty;

#endregion

public override void ItemUpdated(SPItemEventProperties properties)

{

EventHandlerConstructor();

if (properties.ListItem[ApprovalColumnName].ToString() == Strings.InDraftStatus)

{

DownloadItem(properties);

}

private void EventHandlerConstructor()

{

TemporaryFolder = Strings.TemporaryFolderKey;

ApprovalColumnName = Strings.ApprovalColumnKey;

}

private void DownloadItem(SPItemEventProperties properties)

{

SPFile File = properties.ListItem.File;

string FileTempName = DateTime.Now.ToString(Strings.DateFormat) +

properties.ListItem[Strings.IDColumn].ToString() +

properties.ListItem[Strings.NameColumn].ToString();

if (File.Name.ToLower().EndsWith(Strings.DocxExtension) ||

File.Name.ToLower().EndsWith(Strings.DocExtension))

{

byte[] Filebytes = File.OpenBinary(SPOpenBinaryOptions.None);

DirectoryInfo TempDirectory = new DirectoryInfo(TemporaryFolder);

if (!TempDirectory.Exists)

{

TempDirectory.Create();

}

FileStream TempFileOnDisk = new FileStream(TemporaryFolder + FileTempName,

FileMode.CreateNew);

BinaryWriter bWriter = new BinaryWriter(TempFileOnDisk);

foreach (byte b in Filebytes)

{

bWriter.Write(b);

}

bWriter.Flush();

bWriter.Close();

TempFileOnDisk.Close();

bool SignatureAdded = AddDigitalSignature(FileTempName, properties);

if (SignatureAdded)

{

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = true;

WriteFileAgain(properties, FileTempName);

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = false;

}

private bool AddDigitalSignature(string FileTempName, SPItemEventProperties properties)

{

object TempFilePath = TemporaryFolder + FileTempName;

object Visible = false;

object readonlyfile = false;

try

{

object missing = System.Reflection.Missing.Value;

Microsoft.Office.Interop.Word.ApplicationClass wordapp = new

Microsoft.Office.Interop.Word.ApplicationClass();

Microsoft.Office.Interop.Word.Document wordDocument = wordapp.Documents.Open(ref

TempFilePath, ref missing,

ref readonlyfile, ref missing, ref missing,

ref missing, ref missing, ref missing,

ref Visible, ref missing, ref missing,

ref missing, ref missing);

SignatureSet signatureSet = wordDocument.Signatures;

Signature objSignature = signatureSet.Add();

if (objSignature == null)

{

DocumentNotSigned(properties);

return false;

}

else

{

signatureSet.Commit();

object saveChanges = true;

wordDocument.Close(ref saveChanges, ref missing, ref missing);

wordapp.Quit(ref missing, ref missing, ref missing);

return true;

}

catch

{

return false;

}

private void WriteFileAgain(SPItemEventProperties properties, string TemporaryFile)

{

SPFile currentFile = properties.ListItem.File;

string TempFilePath = TemporaryFolder+ TemporaryFile;

FileStream st = new FileStream(TempFilePath, FileMode.Open);

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = true;

currentFile.CheckOut();

currentFile.SaveBinary(st);

this.DisableEventFiring();

currentFile.CheckIn(string.Empty);

currentFile.Publish(string.Empty);

currentFile.Approve(string.Empty);

st.Close();

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = false;

this.EnableEventFiring();

FileInfo deletedfile = new FileInfo(TemporaryFolder + TemporaryFile);

deletedfile.Delete();

}

private void DocumentNotSigned(SPItemEventProperties properties)

{

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = true;

SPFile currentFile = properties.ListItem.File;

if (currentFile.CheckOutStatus == SPFile.SPCheckOutStatus.None)

{

currentFile.CheckOut();

}

this.DisableEventFiring();

currentFile.CheckIn(string.Empty);

currentFile.Publish(string.Empty);

currentFile.Deny(string.Empty);

properties.ListItem.ParentList.ParentWeb.AllowUnsafeUpdates = false;

this.EnableEventFiring();

}