Realize PDF to picture conversion with C ＃

         This week I came across a demand , Due to the company's system framework , It cannot directly display the information returned by the third party pdf( Explain , Returned by the third party pdf Is to bring the signature information ( That is to say pdf Signature pictures are added to )), Need to put pdf Turn it into a picture for display , But in the process of doing it, I stepped on a lot of thunder . Finally, use third-party plug-ins PDFRender4NET

1    Third party plug-ins PdfiumViewer( shortcoming , Missing signature information )

          First, I tried a third-party plug-in PdfiumViewer, The code is simple , There are a lot of them on the Internet demo, Copy the code and modify it , It's done in three or two , Tried it on , Indeed, it can be achieved pdf Transfer pictures , But when I finish writing the business code , When running on a business system , Find out , Mama of , It's careless , The converted image has lost its signature information . Here is some of the code I have slightly modified ：

public class PdfToImageHelper
    {
        /// <summary>
        /// pdf Turn picture (base64 Format string )
        /// </summary>
        /// <param name="pdfBase64String">pdf Corresponding base64 character string </param>
        /// <returns>Pdf If there are more than one page , Just return multiple pictures (base64 String collection )</returns>
        public static List<string> GetBase64StringArray(string pdfBase64String)
        {
            if (pdfBase64String==null|| pdfBase64String.Length==0) return null;
            List<string> base64StringList = new List<string>();
            byte[] buffer=Convert.FromBase64String(pdfBase64String);
            if (buffer == null || buffer.Length == 0) return base64StringList;
            MemoryStream ms = new MemoryStream(buffer);
            var pdfDocument = PdfiumViewer.PdfDocument.Load(ms);
            for (int index = 0; index <pdfDocument.PageCount; index++)
            {
                Image image = pdfDocument.Render(index, (int)pdfDocument.PageSizes[index].Width, (int)pdfDocument.PageSizes[index].Height, 300, 300, false);
                string base64Str=ImageToBase64String(image);
                if (base64Str != null && base64Str.Length > 0)
                {
                    base64StringList.Add(base64Str);
                }
            }
            // Free up streaming resources 
            return base64StringList;
        }

        /// <summary>
        /// Image Object turn base64 character string 
        /// </summary>
        /// <param name="Picture"></param>
        /// <returns></returns>
        private static string ImageToBase64String(Image Picture)
        {
            MemoryStream ms = new MemoryStream();
            if (Picture == null)
                return null;
            Picture.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            byte[] BPicture = new byte[ms.Length];
            BPicture = ms.GetBuffer();
            // Free up streaming resources 
            return Convert.ToBase64String(BPicture);
        }
    }

call ：List<string>  imageBase64StringList=PdfToImageHelper.GetBase64StringArray("pdf Corresponding base64 character string ");

2  Third party plug-ins Spire.pdf ( shortcoming ： charge , There is a free version of , however pdf There is a page limit for converting to pictures ( most 3 page ) , And the converted image is very blurred )

Use PdfiumViewer No, after , Start using Spire.pdf, adopt vistual studio Of nuget You can get dll, Here's the picture ：

first Spire.PDF Is the charge , The watermark information shown in the following figure will be carried on the upper left corner of the converted image

  the second FreeSpire.PDF It's free. , however pdf If exceeded 3 page , Only turn forward 3 page , The following conversion is all blank pages

The code is not posted , There are many on the Internet demo

3    Third party plug-ins PDFRender4NET(O2S.Components.PDFRender4NET.dll, The version information is shown in the figure below )

  The code I slightly modified is posted below ：

using O2S.Components.PDFRender4NET;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Linq;
using System.Text;

namespace iih.gdrmh.ca.PatientSign.bp
{
    public class PdfToImageHelper
    {
        public static List<string> GetBase64StringArrayByPdfPath(string pdfPath)
        {
            if (pdfPath == null || pdfPath.Length == 0) return null;
            List<string> base64StringList = new List<string>();
            PDFFile pdfFile = PDFFile.Open(pdfPath);
            for (int index =0; index <pdfFile.PageCount; index++)
            {
                Bitmap pageImage = pdfFile.GetPageImage(index, 56 * 10);
                string base64Str = BitmapToBase64String(pageImage);
                if (base64Str != null && base64Str.Length > 0)
                {
                    base64StringList.Add(base64Str);
                }
            }
            pdfFile.Dispose();
            return base64StringList;
        }

        private static string ImageToBase64String(Image Picture)
        {
            MemoryStream ms = new MemoryStream();
            if (Picture == null)
                return null;
            Picture.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            byte[] BPicture = new byte[ms.Length];
            BPicture = ms.GetBuffer();
            return Convert.ToBase64String(BPicture);
        }


        private static string BitmapToBase64String(Bitmap bitmap)
        {
            // 1. First the BitMap Convert to memory stream 
            MemoryStream ms = new MemoryStream();
            bitmap.Save(ms, ImageFormat.Png);
            ms.Seek(0, SeekOrigin.Begin);
            // 2. Then the memory is transferred to byte[] And back to 
            byte[] bytes = new byte[ms.Length];
            ms.Read(bytes, 0, bytes.Length);
            ms.Flush();
            ms.Close();
            ms.Dispose();
            return Convert.ToBase64String(bytes);
        }


    }
}

call ：List<string>  imageBase64StringList=PdfToImageHelper.GetBase64StringArrayByPdfPath("pdf The corresponding file path ");

Finally found , The converted image , The signature information is still , The sharpness ratio of the converted picture FreeSpire.PDF Still high

expand ：

Go to stack overflow Search discovery ,pdf There are many ways to convert pictures , But the most recommended is Ghostscript.NET. github The address is ：https://github.com/jhabjan/Ghostscript.NET   demo Code ：https://github.com/jhabjan/Ghostscript.NET/blob/master/Ghostscript.NET.Samples/Samples/RasterizerSample1.cs

stack overflow Reference link ：

1  Convert Pdf to Image C# .NET - Stack Overflow

2  Converting pdf to image using c# and Ghostscript - Stack Overflow

3  asp.net - Convert PDF file to images using C# - Stack Overflow