Re: Adding connectors to obejct exported from AutoCAD.

Ok so as I told you the code provided work perfectly in Revit 2016

To make the same approach from the Project document use the following code:

#region Namespaces

using System;
using System.Text;
using System.Linq;
using System.Xml;
using System.Reflection;
using System.ComponentModel;
using System.Collections;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Media.Imaging;
using System.Windows.Forms;
using System.IO;

using Autodesk.Revit.ApplicationServices;
using Autodesk.Revit.Attributes;

using Autodesk.Revit.DB;
using Autodesk.Revit.DB.Events;
using Autodesk.Revit.DB.Architecture;
using Autodesk.Revit.DB.Structure;
using Autodesk.Revit.DB.Mechanical;
using Autodesk.Revit.DB.Electrical;
using Autodesk.Revit.DB.Plumbing;

using Autodesk.Revit.UI;
using Autodesk.Revit.UI.Selection;
using Autodesk.Revit.UI.Events;

//using Autodesk.Revit.Collections;
using Autodesk.Revit.Exceptions;
using Autodesk.Revit.Utility;

using RvtApplication = Autodesk.Revit.ApplicationServices.Application;
using RvtDocument = Autodesk.Revit.DB.Document;

#endregion

namespace RevitAddinCS2
{
    [Transaction(TransactionMode.Manual)]
    [Regeneration(RegenerationOption.Manual)]
    public class ExtCmd : IExternalCommand
    {
        #region Cached Variables

        private static ExternalCommandData _cachedCmdData;

        public static UIApplication CachedUiApp
        {
            get
            {
                return _cachedCmdData.Application;
            }
        }

        public static RvtApplication CachedApp
        {
            get
            {
                return CachedUiApp.Application;
            }
        }

        public static RvtDocument CachedDoc
        {
            get
            {
                return CachedUiApp.ActiveUIDocument.Document;
            }
        }

        #endregion

        #region IExternalCommand Members

        public Result Execute(ExternalCommandData cmdData, ref string msg, ElementSet elemSet)
        {
            _cachedCmdData = cmdData;

            try
            {
                FilteredElementCollector fam = new FilteredElementCollector(CachedDoc).OfClass(typeof(Family));
                var fams = from family in fam
                           where (family.Name == "ImportedObj_corrected")
                           select family;

                List<Family> fa= fams.Cast<Family>().ToList();

                foreach (Family f in fa)
                {
                    if (f.IsEditable)
                    {
                        Document familyDoc = CachedDoc.EditFamily(f);
                        //TODO: add your code below.
                        FilteredElementCollector importCAD = new FilteredElementCollector(familyDoc).OfClass(typeof(ImportInstance));
                        ElementId ImportedObj = importCAD.FirstElementId();

                        if(AddConnectorToFamily(familyDoc, ImportedObj))
                        {
                            familyDoc.LoadFamily(CachedDoc,new FamilyOption());
                        }
                    }
                }

                return Result.Succeeded;
            }
            catch (Exception ex)
            {
                msg = ex.ToString();
                return Result.Failed;
            }
        }

        public bool AddConnectorToFamily(Document famDoc, ElementId importedId)
        {
            //Connector Values.
            XYZ connNormal = new XYZ(0, 0, 1);
            XYZ connDirection = new XYZ(1, 0, 0);
            XYZ connOrigin = new XYZ(-24.022405238, -59.669659519, 9.583333333);

            PlanarFace pf = null;

            Options opts = famDoc.Application.Create.NewGeometryOptions();
            opts.DetailLevel = ViewDetailLevel.Fine;
            opts.ComputeReferences = true;

            //This is a little redundant.
            Element e = famDoc.GetElement(importedId);
            ImportInstance impInst = e as ImportInstance;

            //To access the Geometry of the Imported DWG block
            //We need to dig into it a little bit.
            GeometryElement impGeo = impInst.get_Geometry(opts);

            foreach (GeometryObject impGeoObj in impGeo)
            {
                GeometryInstance symInst = impGeoObj as GeometryInstance;
                GeometryElement symEle = symInst.SymbolGeometry;

                using (Transaction t = new Transaction(famDoc, "edit"))
                {
                    t.Start();
                    foreach (GeometryObject symObj in symEle)
                    {
                        Solid solid = symObj as Solid;

                        if (solid != null)
                        {
                            FaceArray fa = solid.Faces;
                            foreach (Face f in fa)
                            {
                                pf = f as PlanarFace;

                                if ((pf != null) && (IsParallel(connDirection, pf.FaceNormal)))
                                {
                                    if (pf.Origin.IsAlmostEqualTo(connOrigin))
                                    {
                                        using (SubTransaction refTrans = new SubTransaction(famDoc))
                                        {
                                            refTrans.Start();

                                            ConnectorElement.CreateDuctConnector(famDoc, DuctSystemType.Global, ConnectorProfileType.Round, pf.Reference, pf.EdgeLoops.get_Item(0).get_Item(0));

                                            refTrans.Commit();

                                        }
                                    }
                                }
                            }
                        }
                    }
                    t.Commit();
                }
            }

            famDoc.Save();
            return true;
        }

        const double _eps = 1.0e-9;

        /// <summary>
        /// Check whether two real numbers are equal
        /// </summary>
        static public bool IsEqual(double a, double b)
        {
            return Math.Abs(a - b) < _eps;
        }

        /// <summary>
        /// Check whether two vectors are parallel
        /// </summary>
        static public bool IsParallel(XYZ a, XYZ b)
        {
            double angle = a.AngleTo(b);
            return _eps > angle || IsEqual(angle, Math.PI);
        }
        #endregion
        class FamilyOption : IFamilyLoadOptions
        {


            bool IFamilyLoadOptions.OnFamilyFound(bool familyInUse, out bool overwriteParameterValues)
            {
                overwriteParameterValues = true;
                return true;
            }

            bool IFamilyLoadOptions.OnSharedFamilyFound(Family sharedFamily, bool familyInUse, out FamilySource source, out bool overwriteParameterValues)
            {
                source = FamilySource.Family;
                overwriteParameterValues = true;
                return true;
            }
        }
    }
}

You can follow the modifications I made to adjust your code.

I also make some correction to the Family insertion point.