using PdfSharp.Drawing;
using PdfSharp.Pdf;
using System;
using System.IO;

string inputFilePath = "C:\\temp\\input.pdf";
string outputFilePath = "C:\\temp\\output-6.2.pdf";

if (File.Exists(outputFilePath))
   File.Delete(outputFilePath);

using var pdfDocument = new PdfDocument();
using var pdfForm = XPdfForm.FromFile(inputFilePath);

pdfForm.PageNumber = 1;

Console.WriteLine($"{inputFilePath} - XPdfForm.PointHeight :  {pdfForm.PointHeight}");
Console.WriteLine($"{inputFilePath} - XPdfForm.PixelHeight :  {pdfForm.PixelHeight}");
Console.WriteLine($"{inputFilePath} - XPdfForm.PointWidth  :  {pdfForm.PointWidth}");
Console.WriteLine($"{inputFilePath} - XPdfForm.PixelWidth  :  {pdfForm.PixelWidth}");

var sourcePageSizeInPoints = new XSize(pdfForm.PointWidth, pdfForm.PointHeight);
var pdfPage = pdfDocument.AddPage();

pdfPage.Width = XUnit.FromPoint(sourcePageSizeInPoints.Width);
pdfPage.Height = XUnit.FromPoint(sourcePageSizeInPoints.Height);

var pageRect = new XRect(0, 0, sourcePageSizeInPoints.Width, sourcePageSizeInPoints.Height);

using var gfx = XGraphics.FromPdfPage(pdfPage);

gfx.Save();
gfx.DrawImage(pdfForm, pageRect);
gfx.Restore();

pdfDocument.Save(outputFilePath);