The problem arises because the memory stream gets implicitly closed when the PdfStamper is closed. To prevent this add pdfStamper.Writer.CloseStream = false; before pdfStamper.Close(); This instructs the stamper not to close the stream.
Without using of a control or form: using (System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(new Bitmap(1, 1))) { SizeF size = graphics.MeasureString(“Hello there”, new Font(“Segoe UI”, 11, FontStyle.Regular, GraphicsUnit.Point)); } Or in VB.Net: Using graphics As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(New Bitmap(1, 1)) Dim size As SizeF = graphics.MeasureString(“Hello there”, New Font(“Segoe UI”, 11, FontStyle.Regular, GraphicsUnit.Point)) End Using