Rewrite code to sign pdf LTV enabled using itextsharp and C#

I need someone to write code (in existing method) to sign pdf documents using itextsharp .net library. The code should be written in C#. public byte[] Sign(byte[] document, X509Certificate2 certificate, ITSAClient tsaClient) { //signing code here return signed_document; } method receives pdf document as byte array that should be signed, certificate to sign with and TSA client and it returns signed document as byte array or null if there was error. Now it returns signed pdf document but it isnt LTV enabled. Signed document must be LTV enabled, signed documents are used for archiving. I've attached c# Visual studio test solution. You need to modify method Sign in [login to view URL] file without adding new references or changing any other part except [login to view URL] file (you can add helper Methods if needeed). When completed i will test method with real world document and certificate and with Adobe reader.