Calling Add-in (C#) Solidworks PDM API

public void GetAddInInfo(ref EdmAddInInfo poInfo, IEdmVault5 poVault, IEdmCmdMgr5 poCmdMgr)
{
       //Specify information to display in the add-in's Properties dialog box
       poInfo.mbsAddInName = "My serial number generator";
       poInfo.mbsCompany = "The name of my company";
       poInfo.mbsDescription = "Implements serial numbers";
       poInfo.mlAddInVersion = 1;
       poInfo.mlRequiredVersionMajor = 5;
       poInfo.mlRequiredVersionMinor = 2;
 
       //Notify the add-in when a file data card button is clicked
       poCmdMgr.AddHook(EdmCmdType.EdmCmd_CardButton);
}
 
public void OnCmd(ref EdmCmd poCmd, ref EdmCmdData[] ppoData)
     {
            //Respond only to a specific button command
            //The button command to respond to begins with "MyButton:" and ends with the name of the 
            //variable to update in the card 
            if (Strings.Left(poCmd.mbsComment, 9) == "MyButton:")
            {
                //Get the name of the variable to update. 
                string VarName = null;
                VarName = Strings.Right(poCmd.mbsComment, Strings.Len(poCmd.mbsComment) - 9);
 
                //Let the user select the file whose path will be copied to the card variable
                EdmVault5 vault = default(EdmVault5);
                vault = (EdmVault5)poCmd.mpoVault;
                IEdmStrLst5 PathList = default(IEdmStrLst5);
                PathList = vault.BrowseForFile(poCmd.mlParentWnd, (int)EdmBrowseFlag.EdmBws_ForOpen + (int)EdmBrowseFlag.EdmBws_PermitVaultFiles, "", "", "", "", "Select File for " + VarName);
 
                if ((PathList != null))
                {
                    string path = null;
                    path = PathList.GetNext(PathList.GetHeadPosition());
 
                    //Store the path in the card variable 
                    IEdmEnumeratorVariable5 vars = default(IEdmEnumeratorVariable5);
                    vars = (IEdmEnumeratorVariable5)poCmd.mpoExtra;
                    object VariantPath = null;
                    VariantPath = path;
                    vars.SetVar(VarName, "", VariantPath);
                }
            }
 
            return;
     }