Daniel:
Confusion is what add-ins are all about from my perspective, as I have been wanting to move this code into an add-in for over a year. Perhaps the difficulty is my use of .NET 2015 Express (Community, etc).
Thanks for your replies, and I'm sure I must be missing something. The question is, what? Without updated manuals for versions 2015 of Inventor, and/or potential trouble with using VS Express 2015 it has been really difficult to get this going.
I started the project with this add-in project. 
I have selected two options for my project properties.
1. I have specified a build output path for the project with regard ro the compilation.

2. Under debug, I have specified to start an external program, ie: Inventor 2015

The program is: C:\Program Files\Autodesk\Inventor 2015\Bin\inventor.exe
You can see, I have the following project references:

Below is my output folder, and yes, I see an .exe, not a .dll.

When I build the project, I get this error:

And this output:

Truncated line: 1>C:\Program Files (x86)\MSBuild\14.0\bin\Microsoft.Common.CurrentVersion.targets(4714,5): error MSB3073: mt.exe -manifest "Z:\VSProjects\InventorAddIn3\InventorAddIn3\InventorAddIn3.X.manifest" -outputresource:"C:\Users\sanderson\AppData\Roaming\Autodesk\ApplicationPlugins\StampDrawing\StampDrawing.exe";#2" exited with code 9009.
As I said earlier in the post, I pretty much followed this post to get things going:
http://forums.autodesk.com/t5/inventor-customization/inventor-add-in-templates-for-2015/td-p/5235767
Finally, I have pasted my code below:
Imports System.IO
Imports System.Runtime.InteropServices
Public Class StampDrawing
Shared Sub main()
Dim frm As New Form1
frm.Show()
End Sub
End Class
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
Dim dirn As String = "c:\temp"
Dim filn As String = ""
If Len(txtStampText) > 0 Then
filn = "txtStampText.txt"
End If
' Check to see if c:\temp exists
' Check to see if c:\temp\txtStampText.txt exists
Dim fullfilen As String = dirn & "\" & filn
If File.Exists(fullfilen) = True Then
MsgBox(fullfilen)
' Import contents of c:\temp\txtStampText.txt to txtStampText
Dim objStreamReader As StreamReader
Dim strline As String = ""
objStreamReader = New StreamReader(fullfilen)
strline = objStreamReader.ReadLine
Do While Not strline Is Nothing
txtStampText.Text = strline
Loop
objStreamReader.Close()
End If
End Sub
Private Sub cmdPlot_Click(sender As Object, e As EventArgs) Handles cmdPlot.Click
' Export contents of txtStampText to c:\temp\txtStampText.txt
' Define application
Dim oApp As Inventor.Application = GetObject(, "Inventor.Application")
Dim oDoc As Inventor.DrawingDocument = oApp.ActiveDocument
' Define sheets
Dim oSheets As Inventor.Sheets = oDoc.Sheets
Dim oSheet As Inventor.Sheet = oDoc.Sheets.Item(1)
' Define print manager
Dim oPM As Inventor.DrawingPrintManager = oDoc.PrintManager
' Get sheet size
Dim xx As Integer
Dim xy As Integer
Select Case oSheet.Size
Case Inventor.DrawingSheetSizeEnum.kADrawingSheetSize
xx = (6 * 2.54)
xy = (3.12 * 2.54)
Case Inventor.DrawingSheetSizeEnum.kBDrawingSheetSize
xx = (12 * 2.54)
xy = (3.12 * 2.54)
Case Inventor.DrawingSheetSizeEnum.kCDrawingSheetSize
xx = (17 * 2.54)
xy = (3.12 * 2.54)
Case Inventor.DrawingSheetSizeEnum.kDDrawingSheetSize
xx = (29 * 2.54)
xy = (3.12 * 2.54)
Case Inventor.DrawingSheetSizeEnum.kEDrawingSheetSize
xx = (37 * 2.54)
xy = (3.12 * 2.54)
End Select
For Each oSheet In oSheets
oSheet.Activate()
' Create a new sketch on the active sheet
Dim oSketch As Inventor.DrawingSketch = oDoc.ActiveSheet.Sketches.Add
' Open sketch for edit so the texhbox can be created
oSketch.Edit()
Dim oTG As Inventor.TransientGeometry = oApp.TransientGeometry
Dim sText As String
sText = txtStampText.Text
sText = "<StyleOverride Font='Arial' Bold='True' Italic='True' FontSize='.7'>" & sText & "</StyleOverride>"
Dim oTextBox As Inventor.TextBox = oSketch.TextBoxes.AddFitted(oTG.CreatePoint2d(xx, xy), sText)
oSketch.ExitEdit()
' Requires plot to activate text
oPM.PrintToFile("c:\temp\tmpinventor.plot")
' Predefine printers
Dim PRN As String
PRN = "\\PS64\HP Color LaserJet M750dn"
Dim PLT As String
PLT = "\\PS64\HP T2500"
oPM.ScaleMode = Inventor.PrintScaleModeEnum.kPrintFullScale
oPM.PrintRange = Inventor.PrintRangeEnum.kPrintAllSheets
Select Case oSheet.Size
Case Inventor.DrawingSheetSizeEnum.kA4DrawingSheetSize
oPM.Printer = PRN
oPM.PaperSize = Inventor.PaperSizeEnum.kPaperSizeLetter
oPM.Orientation = Inventor.PrintOrientationEnum.kLandscapeOrientation
Case Inventor.DrawingSheetSizeEnum.kBDrawingSheetSize
oPM.Printer = PRN
oPM.PaperSize = Inventor.PaperSizeEnum.kPaperSize11x17
oPM.Orientation = Inventor.PrintOrientationEnum.kLandscapeOrientation
Case Inventor.DrawingSheetSizeEnum.kCDrawingSheetSize
oPM.Printer = PLT
oPM.PaperSize = Inventor.PaperSizeEnum.kPaperSizeCSheet
oPM.Orientation = Inventor.PrintOrientationEnum.kLandscapeOrientation
Case Inventor.DrawingSheetSizeEnum.kDDrawingSheetSize
oPM.Printer = PLT
oPM.PaperSize = Inventor.PaperSizeEnum.kPaperSizeDSheet
oPM.Orientation = Inventor.PrintOrientationEnum.kLandscapeOrientation
Case Inventor.DrawingSheetSizeEnum.kEDrawingSheetSize
oPM.Printer = PLT
oPM.PaperSize = Inventor.PaperSizeEnum.kPaperSizeESheet
oPM.Orientation = Inventor.PrintOrientationEnum.kLandscapeOrientation
End Select
oPM.SubmitPrint()
oSketch.Delete()
Next
End Sub
End Class