Hey there,
I have spent a few hours trying to resolve this problem, however I cannot find anything wrong with what I have done in contrast to what has been suggested. I've found a few different forum posts and different websites, but the following basically sums everything up (
viewtopic.php?f=2&t=2306).
From my understanding, we can utilize the Section.AddImage() method for adding an existing PDF file into a MigraDoc document section. I have wrestled and searched for an answer, but when I do this, all that appears is a red rectangle with an X through it:

From reading, I found people were experiencing this (along with some text saying "Image not found.") when the PDF file or image file could not be found. I determined that this was not the case by providing a fake path to the AddImage() method. When doing so, I did not receive a red X and simply received the "Image not found." error message on the generated PDF.
I further read that you can define the page you want to add as an image by appending "#" followed by the page number in the path passed to AddImage(). I have tested with a path of "C:\test.pdf" and "C:\test.pdf#1" with no difference in the result.
Here is the code I have so far. I can confirm 100% that i.DrawingFilePath exists and that C:\test.pdf exists. Technically in the following I am not using the first bit of code (the PDFsharp code), it is remnant from trying to solve this problem. Perhaps I am going down the wrong path with the code, so, my
only requirement is to be able to take an existing PDF file and insert it into a MigraDoc - I need this existing PDF file added so I can later overlay a text box on it.
Any help is greatly appreciated and thank you in advance for any assistance.
Code:
Dim pdfDocument As PdfSharp.Pdf.PdfDocument = PdfSharp.Pdf.IO.PdfReader.Open(i.DrawingFilePath)
Dim pdfPage As PdfSharp.Pdf.PdfPage = pdfDocument.Pages(0)
Dim gfx As PdfSharp.Drawing.XGraphics = PdfSharp.Drawing.XGraphics.FromPdfPage(pdfPage)
gfx.MUH = PdfSharp.Pdf.PdfFontEncoding.Unicode
gfx.MFEH = PdfSharp.Pdf.PdfFontEmbedding.Default
Dim doc As MigraDoc.DocumentObjectModel.Document = New MigraDoc.DocumentObjectModel.Document
Dim sec As MigraDoc.DocumentObjectModel.Section = doc.AddSection
Dim img As MigraDoc.DocumentObjectModel.Shapes.Image = sec.AddImage("C:\test.pdf#1")
img.RelativeHorizontal = MigraDoc.DocumentObjectModel.Shapes.RelativeHorizontal.Page
img.RelativeVertical = MigraDoc.DocumentObjectModel.Shapes.RelativeVertical.Page
img.WrapFormat.Style = MigraDoc.DocumentObjectModel.Shapes.WrapStyle.Through
Dim docRenderer As MigraDoc.Rendering.DocumentRenderer = New MigraDoc.Rendering.DocumentRenderer(doc)
docRenderer.PrepareDocument()
Dim pageCount As Integer = docRenderer.FormattedDocument.PageCount
Dim printDoc As MigraDoc.Rendering.Printing.MigraDocPrintDocument = New MigraDoc.Rendering.Printing.MigraDocPrintDocument
printDoc.PrinterSettings = printerDialog.PrinterSettings
printDoc.Renderer = docRenderer
printDoc.Print()