AddCustomObjectAsMetadataSignature.cs

// For complete examples and data files, please go to https://github.com/groupdocs-signature/GroupDocs.Signature-for-.NET
// setup Signature configuration
SignatureConfig signConfig = new SignatureConfig
{
    StoragePath = @"c:\GroupDocs\Storage",
    OutputPath = @"c:\GroupDocs\Output"
};
// instantiate the signature handler
SignatureHandler handler = new SignatureHandler(signConfig);
// setup key and passphrase
string key = "1234567890";
string salt = "1234567890";
// create data encryption
IDataEncryption encryption = new SymmetricEncryption(SymmetricAlgorithmType.Rijndael, key, salt);
// setup options with text of signature
ImagesMetadataSignOptions signOptions = new ImagesMetadataSignOptions();
// create custom object
DocumentSignature signature = new DocumentSignature()
{
    ID = Guid.NewGuid().ToString(),
    Author = Environment.UserName,
    Signed = DateTime.Now,
    DataFactor = 11.22M
};
ushort imgsMetadataId = 41996;
// add custom object to the sigature collection
ImageMetadataSignature mdDocument = signOptions.AddSignature(imgsMetadataId, signature);
// set encryption
mdDocument.DataEncryption = encryption;
// sign document
string signedPath = handler.Sign<string>(@"sample.jpg", signOptions,
    new SaveOptions { OutputType = OutputType.String, OutputFileName = "SignedImage.jpg" });
Console.WriteLine("Signed file's path is: " + signedPath);

SearchSignature.cs

// For complete examples and data files, please go to https://github.com/groupdocs-signature/GroupDocs.Signature-for-.NET
// setup configuration
SignatureConfig signConfig = new SignatureConfig
{
    StoragePath = @"c:\GroupDocs\Storage",
    OutputPath = @"c:\GroupDocs\Output"
};
// instantiate the signature handler
SignatureHandler handler = new SignatureHandler(signConfig);
// setup search options
PdfSearchQRCodeOptions searchOptions = new PdfSearchQRCodeOptions();
// specify as true to search all pages of a document
searchOptions.SearchAllPages = true;
// search document
SearchResult result = handler.Search("SignedQRCode.pdf", searchOptions);
// output signatures
List<QRCodeSignature> signatures = result.ToList<QRCodeSignature>();
foreach (QRCodeSignature signature in signatures)
{
    Console.WriteLine("Found QRCode signature: {0} with text {1} on page {2}", signature.EncodeType.TypeName, signature.Text, signature.PageNumber);
}