c# pdf转图片

需安装nuget包：

<package id="PdfiumViewer" version="2.13.0.0" targetFramework="net45" />

<package id="HiraokaHyperTools.PdfiumViewer.Native.Windows" version="0.1.5637" targetFramework="net45" />

using PdfiumViewer;
using System.Collections.Generic;
using System.Drawing.Imaging;
using System.IO;

namespace IDH.Common.Utility
{
    public partial class PDFHelper
    {
        /// <summary>
        /// <param name="filePath">pdf文件路径</param> 
        /// <param name="imageSaveNameList">图片名</param> 
        /// <param name="image">文件格式：Jpeg  （转换后文件格式，如：Jpeg，Png等）</param> 
        /// </summary> 
        public static List<string> PdfToPic(string filePath, string directoryPath, List<string> imageSaveNameList, ImageFormat image)
        {
            var imagePathList = new List<string>();
            var pdf = PdfDocument.Load(filePath);
            var pdfpage = pdf.PageCount;
            for (int i = 0; i < pdfpage; i++)
            {
                var outFilePath = directoryPath + "\\" + imageSaveNameList[i];
                if (string.IsNullOrWhiteSpace(Path.GetExtension(outFilePath)))
                {
                    outFilePath += "." + image.ToString();
                }
                RenderPage(pdf, i, outFilePath, image);

                imagePathList.Add(outFilePath);
            }

            pdf.Dispose();

            return imagePathList;

        }

        /// <summary>
        /// 渲染图片
        /// </summary>
        /// <param name="document"></param>
        /// <param name="pageNumber"></param>
        /// <param name="size"></param>
        /// <param name="outputPath"></param>
        /// <param name="mat"></param>
        /// <param name="dpi"></param>
        private static void RenderPage(PdfDocument document, int pageNumber, string outputPath, ImageFormat mat, int dpi = 300)
        {
            using (var stream = new FileStream(outputPath, FileMode.Create))
            using (var image = GetPageImage(pageNumber, document, dpi))
                image.Save(stream, mat);
        }

        /// <summary>
        /// 根据页数转换图片
        /// </summary>
        /// <param name="pageNumber"></param>
        /// <param name="size"></param>
        /// <param name="document"></param>
        /// <param name="dpi"></param>
        /// <returns></returns>
        private static System.Drawing.Image GetPageImage(int pageNumber, PdfDocument document, int dpi)
        {
            return document.Render(pageNumber, dpi, dpi, PdfRenderFlags.CorrectFromDpi);
        }
    }
}