Text added with iText to PDF appears invisible on some pages

Question

I have the following function, which I am using to add a rotated date on the right side of each page of a PDF containing multiple engineering drawings, using iText:

Action<string, string> InsertDateStamp =
(newFile, sourcePdfPath) =>
{
    string dateStamp = DateTime.Now.ToString("dd-MMM-yyyy");
    
    using (var pdfReader = new iText.Kernel.Pdf.PdfReader(sourcePdfPath))
    using (var pdfWriter = new iText.Kernel.Pdf.PdfWriter(newFile))
    using (var pdfDoc = new iText.Kernel.Pdf.PdfDocument(pdfReader, pdfWriter))
    {
        var numPages = pdfDoc.GetNumberOfPages();
        
        for (int pageNum = 1; pageNum <= numPages; pageNum++)
        {
            var page = pdfDoc.GetPage(pageNum);
            
            var pdfCanvas = new PdfCanvas(page.NewContentStreamBefore(), page.GetResources(), pdfDoc);

            var canvas = new iText.Layout.Canvas(pdfCanvas, page.GetPageSize());

            canvas.SetFontColor(iText.Kernel.Colors.ColorConstants.BLACK);
            canvas.SetFontSize(14);
            canvas.SetFont(iText.Kernel.Font.PdfFontFactory.CreateFont(iText.IO.Font.Constants.StandardFonts.TIMES_ROMAN));
            canvas.ShowTextAligned(new iText.Layout.Element.Paragraph(dateStamp), 785, 300, pageNum, iText.Layout.Properties.TextAlignment.CENTER, iText.Layout.Properties.VerticalAlignment.MIDDLE, 1.5708f);
            
            pdfCanvas.Release();
        }
        
        pdfDoc.Close();
        pdfReader.Close();
        pdfWriter.Close();
    }
};

This code works most of the time, but for some reason on some pages the added text is not visible. It is THERE, as I can select it and copy and paste it into notepad, but the text is just not visible on the page.

For example:

This only occurs on some pages, and I cannot figure out why, or what is wrong with the code in question...

Any help would be greatly appreciated.

Thanks!

Answer 1

Finally, after much messing around, managed to get it working:

    var over = new PdfCanvas(page);
    over.SetFillColorRgb(0, 0, 0);
    
    var p = new iText.Layout.Element.Paragraph(dateStamp).SetFont(iText.Kernel.Font.PdfFontFactory.CreateFont(iText.IO.Font.Constants.StandardFonts.TIMES_ROMAN)).SetFontSize(14);
    new iText.Layout.Canvas(over, page.GetPageSize()).ShowTextAligned(p, 785, 300, pageNum, iText.Layout.Properties.TextAlignment.CENTER, iText.Layout.Properties.VerticalAlignment.MIDDLE, 1.5708f);

It makes no sense to me, but hey, it works....