Problem with autofill Fields in interactive pdf via C#.

Hello,

I have problem with autofill Fields in interactive pdf via C#.

Method myFields.GetEnumerator() returns empty enumerator.

IEnumerator myEnumerator = myFields.GetEnumerator();

           String FORM_NAME = Application.StartupPath + "\\PIT-11(23)_v1-0E_2016.pdf";
            
            CAcroApp acroApp = new AcroAppClass();            
            acroApp.Show();
            CAcroAVDoc avDoc = new AcroAVDocClass();
            // Open the pdf
            if (!avDoc.Open(FORM_NAME, ""))
            {
                string szMsg = "Cannot open" + FORM_NAME + ".\n";
                Console.WriteLine(szMsg);
                return;
            }
            
            try
            {
                // Create a IAFormApp object, so that we can access the form fields in  the open document
                IAFormApp formApp = new AFormAppClass();
                IFields myFields = (IFields)formApp.Fields;
                IEnumerator myEnumerator = myFields.GetEnumerator();//EMPTY ENUMERATOR!!!!!
                while (myEnumerator.MoveNext())
                {
                    IField myField = (IField)myEnumerator.Current;
                    // If the field is "Name", set it's value to "John Doe"
                    if (myField.Name == "Name")
                    {
                        myField.Value = "John Doe";
                        break;
                    }
                }
                return;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }