UserControl does not contain a defination for Application

Question

I am trying to do a search operation in active word document on a button click. And getting a error in my code is

The button is on a custom task pane

Error CS1061 'UserControl1' does not contain a definition for 'Application' and no accessible extension method 'Application' accepting a first argument of type 'UserControl1' could be found (are you missing a using directive or an assembly reference?) WordAddIn1 c:\users\veroot\source\repos\WordAddIn1\WordAddIn1\UserControl1.cs 29 Active

And the code is

private void button1_Click(object sender, EventArgs e)
    {
        object findText = textBox1.Text;
        object missing = System.Type.Missing;

        Word.Document document = this.Application.ActiveDocument;
        Word.Range rng = document.Range(0, Type.Missing);


        rng.Find.Highlight = 0;
        rng.Find.Forward = true;
        do
        {
            if (rng.HighlightColorIndex == WdColorIndex.wdYellow)
            {

                rng.HighlightColorIndex = WdColorIndex.wdRed;
                rng.Font.ColorIndex = WdColorIndex.wdBlue;
            }
            int intPosition = rng.End;
            rng.Start = intPosition;
        } while (rng.Find.Execute("", missing, missing, missing, missing, missing, true,
            missing, missing, missing, missing, missing, missing, missing, missing));
    }

Answer 1

In a VSTO solution it's only possible to use the keyword this to refer to the host Office application inside the ThisAddin class. In all other classes, including the one for a UserControl, this will refer to that class (the UserControl) and have no relation or connection to the host Office application. So in the case of the code shown in the question, this refers to the UserControl class.

In order to refer to the Office application in which the VSTO add-in is running it's best to use the Globals keyword. For example

 Word.Document doc = Globals.ThisAddIn.Application.ActiveDocument;

or

 Word.Document doc = Globals.ThisAddIn.app.ActiveDocument;

where app is a class-level field in the ThisAddin class - example declaration:

    public partial class ThisAddIn
    {
        public Word.Application app;

which is assigned in ThisAddin_Startup - for example:

    private void ThisAddIn_Startup(object sender, System.EventArgs e)
    {
        app = this.Application;