PDFsharp & MigraDoc Foundation

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

public static void DrawGradientRectangle(string filePath)
{
    using (PdfDocument document = new PdfDocument())
    {
        PdfPage page = document.AddPage();
        XGraphics gfx = XGraphics.FromPdfPage(page);
        XRect rect = new XRect(50, 50, 250, 100); // x, y, width, height

        // Create a red to transparent gradient brush
        XLinearGradientBrush brush = new XLinearGradientBrush(
            rect,
            XColor.FromArgb(255, 255, 0, 0), // Solid Red
            XColor.FromArgb(0, 255, 0, 0),   // Transparent Red
            XLinearGradientMode.Horizontal
        );

        // Draw the rectangle with the gradient brush
        gfx.DrawRectangle(brush, rect);

        // Save the document
        document.Save(filePath);
    }
}

// Call the function and provide the path to save the PDF
DrawGradientRectangle("GradientRectangle.pdf");