Signing PDF from Pkcs11Interop for CKM_ECDSA_SHA256 using SoftHSM 2.2.0 (ECDSA with SHA256) C# .net

I am trying to sign Pdf documents using Pkcs11Interop .net library. I need to use ECDSA encryption algorithm with SHA256 hash algorithm. And I am using SoftHSM 2.2.0 for storing private keys.

I found an CKM enum, CKM_ECDSA_SHA256, which I am passing while creating an object of class mechanism for calling the Sign method of Session.

I am getting the response from the "Signdata" method, however, on opening the Pdf files generated after signing give an error "Signature Invalid". Here is the code snippet for Signdata method call. I don't get any error or exception in the code, however, the pdf as I have mentioned are showing signature invalid.

private Pkcs11 _pkcs11;
private Slot _slot;
private Session _session;

try
{
   _pkcs11 = new Pkcs11(hsmCryptoApi, true);
}
catch (Pkcs11Exception ex)
{
   if (ex.RV == CKR.CKR_CANT_LOCK)
      _pkcs11 = new Pkcs11(hsmCryptoApi, false);
   else
       throw ex;
}

_slot = FindSlot(_pkcs11, _certificateInformation.TokenLabel);
_session = _slot.OpenSession(true);

using (Mechanism mechanism = new Mechanism(CKM.CKM_ECDSA_SHA256))
{
  _session.Login(CKU.CKU_USER, passowrd);
  byte[] signedHash = _session.Sign(mechanism, GetPrivateKeyHandle(), message);
  _session.Logout();
  return signedHash;
}

private ObjectHandle GetPrivateKeyHandle()
{
  string keyLabel = _certificateInformation.KeyLabel;
  List<ObjectAttribute> searchTemplate = new List<ObjectAttribute>();
  searchTemplate.Add(new ObjectAttribute(CKA.CKA_CLASS, CKO.CKO_PRIVATE_KEY));
  searchTemplate.Add(new ObjectAttribute(CKA.CKA_LABEL, keyLabel));
  List<ObjectHandle> foundObjects = _session.FindAllObjects(searchTemplate);
  return foundObjects[0]; 
}

• Please tell me if SoftHSM 2.2.0 supports ECDSA_P256 with SHA256 or not ??
• If not, then is there any way to enable the support ??
• If it does support, please help me how to fix this ??
• It looks like it want me to pass ECDSA_Param, does anybody have any code snippet for passing the ECDSA_Param