Public Sub OnConnection(ByVal application As Object, ByVal _
  connectMode As ext_ConnectMode, ByVal addInInst As Object, _
  ByRef custom As Array) Implements IDTExtensibility2.OnConnection
    _applicationObject = CType(application, DTE2)
    _addInInstance = CType(addInInst, AddIn)
    ' Pass the applicationObject member variable to the code example.
    OutputWindowTest(_applicationObject)
End Sub

Sub OutputWindowTest(ByVal dte As DTE2)
    ' Create a tool window reference for the Output window
    ' and window pane.
    Dim ow As OutputWindow = dte.ToolWindows.OutputWindow
    Dim owP As OutputWindowPane

    ' Add a new pane to the Output window.
    owP = ow.OutputWindowPanes.Add("A New Pane")
    ' Add a line of text to the new pane.
    owP.OutputString("Some Text")
End Sub

public void OnConnection(object application, ext_ConnectMode 
  connectMode, object addInInst, ref Array custom)
{
    _applicationObject = (DTE2)application;
    _addInInstance = (AddIn)addInInst;
    // Pass the applicationObject member variable to the code example.
    OutputWindowTest(_applicationObject);
}

public void OutputWindowTest(DTE2 dte)
{
    // Create a tool window reference for the Output window
    // and window pane.
    OutputWindow ow = dte.ToolWindows.OutputWindow;
    OutputWindowPane owP;

    // Add a new pane to the Output window.
    owP = ow.OutputWindowPanes.Add("A New Pane");
    // Add a line of text to the new pane.
    owP.OutputString("Some Text");
}

Public Sub OnConnection(ByVal application As Object, ByVal _
  connectMode As ext_ConnectMode, ByVal addInInst As Object, _
  ByRef custom As Array) Implements IDTExtensibility2.OnConnection
    _applicationObject = CType(application, DTE2)
    _addInInstance = CType(addInInst, AddIn)
    ' Pass the applicationObject member variable to the code example.
    writeReadOW(_applicationObject)
End Sub

Sub writeReadOW(ByVal dte As DTE2)
    ' Add-in code.
    ' Create a reference to the Output window.
    ' Create a tool window reference for the Output window
    ' and window pane.
    Dim ow As OutputWindow = dte.ToolWindows.OutputWindow
    Dim owP As OutputWindowPane
    ' Create a reference to the pane contents.
    Dim owPTxtDoc As TextDocument

    ' Select the Build pane in the Output window.
    owP = ow.OutputWindowPanes.Item("Build")
    owP.Activate()
    owPTxtDoc = owP.TextDocument

    ' Put some text in the pane.
    owP.OutputString("Testing 123.")
    ' Retrieve the text contents of the pane.
    MsgBox("Startpoint: " & owPTxtDoc.StartPoint.DisplayColumn)
    MsgBox(owPTxtDoc.StartPoint.CreateEditPoint. _
      GetText(owPTxtDoc.EndPoint))
End Sub

using System.Windows.Forms;
public void OnConnection(object application, ext_ConnectMode 
  connectMode, object addInInst, ref Array custom)
{
    _applicationObject = (DTE2)application;
    _addInInstance = (AddIn)addInInst;
    // Pass the applicationObject member variable to the code example.
    writeReadOW(_applicationObject);
}

public void writeReadOW(DTE2 dte)
{
    // Add-in code.
    // Create a reference to the Output window.
    // Create a tool window reference for the Output window
    // and window pane.
    OutputWindow ow = dte.ToolWindows.OutputWindow;
    OutputWindowPane owP;
    // Create a reference to the pane contents.
    TextDocument owPTxtDoc;
    EditPoint2 strtPt;

    // Select the Build pane in the Output window.
    owP = ow.OutputWindowPanes.Item("Build");
    owP.Activate();
    owPTxtDoc = owP.TextDocument;
            
    // Put some text in the pane.
    owP.OutputString("Testing 123.");
    // Retrieve the text contents of the pane.
    System.Windows.Forms.MessageBox.Show("Startpoint: " + 
      owPTxtDoc.StartPoint.DisplayColumn);
    strtPt = (EditPoint2)owPTxtDoc.StartPoint.CreateEditPoint();
    System.Windows.Forms.MessageBox.Show
      (strtPt.GetText(owPTxtDoc.EndPoint));
}