First page is blackened after adding watermark - pdfsharp

Question

Page is blackened after adding watermark in case of some pdf files . Please see attached image.
What could be the reason , and possible fix.
see the blacked out page image
It does not happen for all the files but for some files only.
Code is here in dotnetfiddle.
var _pdfInBytes = File.ReadAllBytes("c:\\test\\test123.pdf");
string watermarkText = "This watermark text on left side";
var coordinates = new Point(25, 200);
using (var pdfNewDoc = new PdfDocument())
{
using (var pdfImport = PdfReader.Open(new MemoryStream(_pdfInBytes, true), PdfDocumentOpenMode.Import))
{
if (pdfImport.PageCount == 0)
{
return;
}
foreach (var pg in pdfImport.Pages)
{
pdfNewDoc.AddPage(pg);
}
var page = pdfNewDoc.Pages[0];
// overlapping trick #165910
var xOffset = 100.0;
for (var index = 0; index < page.Contents.Elements.Count; index++)
{
var stream = page.Contents.Elements.GetDictionary(index).Stream;
var x = GetMinXOffsetDraft(stream.ToString());
if (xOffset > x)
{
xOffset = x;
}
}
xOffset *= 0.6; // magic number :)
// blank page trick #165910
if (page.CropBox.IsEmpty && !page.MediaBox.IsEmpty)
{
page.CropBox = page.MediaBox;
}
// Get an XGraphics object for drawing beneath the existing content
var gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Prepend);
var tf = new XTextFormatter(gfx);
var xFont = new XFont("Arial", 10, XFontStyle.Regular);
// Get watermark text size
var wmSize = gfx.MeasureString(watermarkText, xFont);
// Middle Y coordinate
var wmY = (gfx.PageSize.Height - wmSize.Width) / 2;
var coords = new XPoint(page.CropBox.Location.X + (xOffset < coordinates.X ? xOffset : coordinates.X),
page.CropBox.Location.Y + (coordinates.Y > wmY ? coordinates.Y : wmY));
// Define a rotation transformation at the center of the page
gfx.TranslateTransform(coordinates.X, coordinates.Y);
gfx.RotateTransform(90);
gfx.TranslateTransform(-coordinates.X, -coordinates.Y);
// Create brush
var brushColor = Color.Red;
var brush1= new XSolidBrush(XColor.FromArgb(brushColor.A, brushColor.R, brushColor.G, brushColor.B));
brush1.Overprint = false;
XBrush brush =
new XSolidBrush(XColor.FromArgb(brushColor.A, brushColor.R, brushColor.G, brushColor.B));
var rect = new XRect(coordinates.X, coordinates.Y, gfx.PageSize.Height - coordinates.Y,
coordinates.X);
tf.DrawString(watermarkText, xFont, brush, rect);
byte[] outputBytes = null;
using (var outStream = new MemoryStream())
{
pdfNewDoc.Save(outStream, false);
outputBytes = outStream.ToArray();
}
File.WriteAllBytes("c:\\test\\test-"+DateTime.Now.ToString("ddmmyyyyhhmmss") +".pdf", outputBytes);
private double GetMinXOffsetDraft(string v)
{
var result = 100.0;
using (var str = new StringReader(v))
{
var s = str.ReadLine();
do
{
var sarr = s?.Split(' ');
if (sarr?.Length == 7 && sarr[6] == "Tm")
{
var x = double.Parse(sarr[4]);
x = x < 0 ? 200 : x;
result = result > x ? x : result;
}
s = str.ReadLine();
} while (s != null);
}
return result;
} var _pdfInBytes = File.ReadAllBytes("c:\\test\\test123.pdf");
string watermarkText = "This watermark text on left side";
var coordinates = new Point(25, 200);
using (var pdfNewDoc = new PdfDocument())
{
using (var pdfImport = PdfReader.Open(new MemoryStream(_pdfInBytes, true), PdfDocumentOpenMode.Import))
{
if (pdfImport.PageCount == 0)
{
return;
}
foreach (var pg in pdfImport.Pages)
{
pdfNewDoc.AddPage(pg);
}
var page = pdfNewDoc.Pages[0];
// overlapping trick #165910
var xOffset = 100.0;
for (var index = 0; index < page.Contents.Elements.Count; index++)
{
var stream = page.Contents.Elements.GetDictionary(index).Stream;
var x = GetMinXOffsetDraft(stream.ToString());
if (xOffset > x)
{
xOffset = x;
}
}
xOffset *= 0.6; // magic number :)
// blank page trick #165910
if (page.CropBox.IsEmpty && !page.MediaBox.IsEmpty)
{
page.CropBox = page.MediaBox;
}
// Get an XGraphics object for drawing beneath the existing content
var gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Prepend);
var tf = new XTextFormatter(gfx);
var xFont = new XFont("Arial", 10, XFontStyle.Regular);
// Get watermark text size
var wmSize = gfx.MeasureString(watermarkText, xFont);
// Middle Y coordinate
var wmY = (gfx.PageSize.Height - wmSize.Width) / 2;
var coords = new XPoint(page.CropBox.Location.X + (xOffset < coordinates.X ? xOffset : coordinates.X),
page.CropBox.Location.Y + (coordinates.Y > wmY ? coordinates.Y : wmY));
// Define a rotation transformation at the center of the page
gfx.TranslateTransform(coordinates.X, coordinates.Y);
gfx.RotateTransform(90);
gfx.TranslateTransform(-coordinates.X, -coordinates.Y);
// Create brush
var brushColor = Color.Red;
var brush1= new XSolidBrush(XColor.FromArgb(brushColor.A, brushColor.R, brushColor.G, brushColor.B));
brush1.Overprint = false;
XBrush brush =
new XSolidBrush(XColor.FromArgb(brushColor.A, brushColor.R, brushColor.G, brushColor.B));
var rect = new XRect(coordinates.X, coordinates.Y, gfx.PageSize.Height - coordinates.Y,
coordinates.X);
tf.DrawString(watermarkText, xFont, brush, rect);
byte[] outputBytes = null;
using (var outStream = new MemoryStream())
{
pdfNewDoc.Save(outStream, false);
outputBytes = outStream.ToArray();
}
File.WriteAllBytes("c:\\test\\test-"+DateTime.Now.ToString("ddmmyyyyhhmmss") +".pdf", outputBytes);
private double GetMinXOffsetDraft(string v)
{
var result = 100.0;
using (var str = new StringReader(v))
{
var s = str.ReadLine();
do
{
var sarr = s?.Split(' ');
if (sarr?.Length == 7 && sarr[6] == "Tm")
{
var x = double.Parse(sarr[4]);
x = x < 0 ? 200 : x;
result = result > x ? x : result;
}
s = str.ReadLine();
} while (s != null);
}
return result;
}