How can I resolve PDF-to-image conversion errors in .NET 8.0 C# on macOS?

Below are some suggestions and explanations to help resolve your issues.

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Error 1 – Base64 FormatException

Issue:
The stack trace indicates that a PDF string is being passed where the library expects a Base64‐encoded representation of the file. In your call to Conversion.SavePng, you’re providing a file path (e.g. "Downloads/testconvert2.pdf") instead of a Base64 string.

Solution:
Read the PDF file into a byte array, then convert it to a Base64 string before calling the method. For example:

CSHARPCopied
using System;
using System.IO;
using PDFtoImage;

namespace PdfToImageApp
{
    class Program
    {
        static void Main(string[] args)
        {
            // Path to your PDF file
            string pdfPath = "Downloads/testconvert2.pdf";
            // Path to save the image
            string outputImagePath = "Downloads/output.png";

            // Read the file and convert it to a Base64 string.
            byte[] pdfBytes = File.ReadAllBytes(pdfPath);
            string pdfBase64 = Convert.ToBase64String(pdfBytes);

            // Convert the first page of the PDF to a PNG.
            // (Ensure you use the correct overload that expects a base64 string.)
            Conversion.SavePng(pdfBase64, outputImagePath);

            Console.WriteLine("PDF to Image conversion completed!");
        }
    }
}

This change ensures that the input provided to the method actually is a valid Base64 string.

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Error 2 – Image.Save Method Overload

Issue:
The error “Cannot resolve method 'Save(string, SixLabors.ImageSharp.Formats.Png.PngEncoder)'” suggests that the ImageSharp API either does not expose that overload or a different method is expected in your installed version.

Solution:
The ImageSharp API may have changed. Instead of calling Save with the encoder, consider one of the following:

1. Use the file extension-based overload – ImageSharp can often infer the encoder from the file extension:

   CSHARPCopied
   image.Save(outputImagePath);

2. Use a specific save method – For example, if available:

   CSHARPCopied
   image.SaveAsPng(outputImagePath);

Check the version and documentation for SixLabors.ImageSharp to see which methods are available. Updating to the latest package version might also resolve any mismatch.

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Error 3 – System.Drawing.ImageFormat on Non-Windows Platforms

Issue:
The warning (CA1416) indicates that System.Drawing APIs are Windows-specific and not supported on macOS. Using Image.Save(..., ImageFormat.Png) triggers this compatibility issue.

Solution:
For cross-platform image processing, use a library that supports macOS. Since you’re already using ImageSharp (via PDFtoImage and SkiaSharp), rely on its API rather than System.Drawing. The approaches in Error 2 are recommended to avoid this warning. Alternatively, if you must use System.Drawing, you could conditionally compile for Windows only, but in a cross-platform .NET 8.0 app, it’s best to migrate to a cross-platform imaging library like SixLabors.ImageSharp.

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Summary

• For your PDFtoImage call:
  Ensure you pass a Base64 representation of the PDF by reading the file as bytes and converting it.

• For saving images with ImageSharp:
  Adjust your code to use a supported overload (such as Save(outputImagePath) or SaveAsPng(outputImagePath)) as per your installed version.

• Avoid using System.Drawing on macOS:
  Stick with cross-platform libraries (ImageSharp or SkiaSharp) to generate and save your image.

Following these steps should help resolve your errors and get you on track for converting PDFs to image thumbnails on macOS with .NET 8.0.