cs azure function merging pdfs

MyMergingFunction.cs

using System.Text;

namespace MyFunction
{
  public static class MyFunction
  {
    public static async Task<IActionResult> ItsMyFunction ()
    {
      // this is needed so that an encoding error is avoided when merging the 2 ca pdfs with PDFSharp
      // https://gunnarpeipman.com/net/no-data-is-available-for-encoding/
      Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
    }
  }
}

PdfBuilder.cs

using PdfSharp.Pdf.IO;
using System.IO;
using PdfSharp.Pdf;
using System.Collections.Generic;

namespace MyFunction
{
  public static class PdfBuilder
  {
    public static byte[] MergePdfs(List<byte[]> pdfs)
    {
      List<PdfDocument> lstDocuments = new List<PdfDocument>();
      foreach (var pdf in pdfs)
      {
        lstDocuments.Add(PdfReader.Open(new MemoryStream(pdf), PdfDocumentOpenMode.Import));
      }

      using (PdfDocument outPdf = new PdfDocument())
      {
        for (int i = 1; i <= lstDocuments.Count; i++)
        {
          foreach (PdfSharp.Pdf.PdfPage page in lstDocuments[i - 1].Pages)
          {
            outPdf.AddPage(page);
          }
        }

        MemoryStream stream = new MemoryStream();
        outPdf.Save(stream, false); // this line wll throw an error if encoding not registered
        byte[] bytes = stream.ToArray();

        return bytes;
      }
    }
  }
}

proj.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <ItemGroup>
    <!-- PDFSharp used  for merging pdfs-->
    <!-- <PackageReference Include="PdfSharp" Version="1.51.5185-beta" /> -->
    <!-- .net standard port of pdfsharp-->
    <PackageReference Include="PdfSharpNetStandard" Version="0.0.14" />
    <!-- required for fixing pdfsharp encoding error -->
    <PackageReference Include="System.Text.Encoding.CodePages" Version="4.5.1" />
  </ItemGroup>
</Project>