一、nuget安装

  <ItemGroup>
    <PackageReference Include="Spire.PDF" Version="10.6.7" />
  </ItemGroup>

二、直接上代码

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.IO;

namespace pdfdemo.Controllers
{
    public class HomeController : Controller
    {
        private readonly ILogger<HomeController> _logger;

        public HomeController(ILogger<HomeController> logger)
        {
            _logger = logger;
        }
        public IActionResult Index()
        {
            var path = $"{AppDomain.CurrentDomain.BaseDirectory}/133634930918199804.pdf";
            var imgPath = $"{AppDomain.CurrentDomain.BaseDirectory}/1336349309181998041.png";
            using (Spire.Pdf.PdfDocument document = new Spire.Pdf.PdfDocument())
            {
                using (var stream = new FileStream(path, FileMode.Open, FileAccess.Read))
                {
                    document.LoadFromStream(stream);
                    using (var memoryStream = new System.IO.MemoryStream())
                    {
                        document.SaveToImageStream(0, memoryStream, "image/png");
                        System.IO.File.WriteAllBytes(imgPath, memoryStream.ToArray());
                    }
                }
            }
            return View();
        }

    }
}

运行效果：