Searching for document signatures excluding external components

GroupDocs.Signature provides boolean property SkipExternal of SearchOptions class to specify if searching process should exclude external signatures (external signatures are the signatures that were added with an 3rd party software and not with GroupDocs.Signature).

Since 19.12 version every time when document is being signed information about document signatures are stored in document’s metadata. Which means that all created signatures by GroupDocs.Signature can be distinguished from an actual document content and IsSignature flag will be set as true. IsSignature property specifies if document component (text/image/barcode/qr-code) is the actual signature or element of document content.

In order to convert signatures added by 3rd party software or by previous version of GroupDocs.Signature, just run Search withSkipExternal property set to false (this is default value) and update IsSignature for each signature returned by the search result.

There are few ways to manipulate with document signature search results:

  • If signature is no longer required it can be removed from the document by Delete method;
  • Signature could be marked as document native content by setting up IsSignature = false property,in this case SkipExternal field will allow Search  method to skip this signature;
  • Signatures that were added before 19.12 are treated as non signatures because information about them are not yet stored in the document. Setting SkipExternal flag to true will exclude these signatures from Searchresult.

Here are the steps to search for signatures and exclude external components of the document with GroupDocs.Signature:

 Following example demonstrates usage of SkipExternalproperty for excluding non actual signatures from search result

using (Signature signature = new Signature("sample_signed.pdf"))
    TextSearchOptions options = new TextSearchOptions()
        // specify SkipExternal value to exclude non signature objects from Search result
        SkipExternal = true,
        // specify search on all pages
        AllPages = false
    // search for text signatures in document
    List<TextSignature> signatures = signature.Search<TextSignature>(options);
    Console.WriteLine("\nSource document contains following text signature(s).");
    // enumerate all signature for output
    foreach (TextSignature textSignature in signatures)
        if (textSignature != null)
            Console.WriteLine($"Found Text signature at page {textSignature.PageNumber} with type [{textSignature.SignatureImplementation}] and text '{textSignature.Text}'.");
            Console.WriteLine($"Location at {textSignature.Left}-{textSignature.Top}. Size is {textSignature.Width}x{textSignature.Height}.");

Updating signatures from GroupDocs.Signature 19.11 and below

Following examples shows the way to mark signatures in document as actual signatures (IsSignature = true)

How to mark signatures in document as actual signatures

 // initialize Signature instance
 using (Signature signature = new Signature("sample_signed.pdf"))
     // define search options to select required signatures om the document
     BarcodeSearchOptions barcodeOptions = new BarcodeSearchOptions();
     QrCodeSearchOptions qrCodeOptions = new QrCodeSearchOptions();
     TextSearchOptions textOptions = new TextSearchOptions();
     // add options to list
     List<SearchOptions> listOptions = new List<SearchOptions>();
     // search for signatures in document
     SearchResult result = signature.Search(listOptions);
     if (result.Signatures.Count > 0)
         Console.WriteLine("\nTrying to update all signatures...");
         // mark all signatures as actual Signatures
         foreach(BaseSignature baseSignature in result.Signatures)
             baseSignature.IsSignature = true;
         // update all found signatures
         UpdateResult updateResult = signature.Update(result.Signatures);
         if(updateResult.Succeeded.Count == result.Signatures.Count)
             Console.WriteLine("\nAll signatures were successfully updated!");
             Console.WriteLine($"Successfully updated signatures : {updateResult.Succeeded.Count}");
             Console.WriteLine($"Not updated signatures : {updateResult.Failed.Count}");
         Console.WriteLine("\nList of updated signatures:");
         int number = 1;
         foreach(BaseSignature temp in updateResult.Succeeded)
             Console.WriteLine($"Signature #{number++}: Type: {temp.SignatureType} Id:{temp.SignatureId}, Location: {temp.Left}x{temp.Top}. Size: {temp.Width}x{temp.Height}");
         Console.WriteLine("No one signature was found.");

More resources

GitHub Examples

You may easily run the code above and see the feature in action in our GitHub examples:

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