1.spire

官方的有水印，通过引用

//private readonly static PdfDocument doc = new PdfDocument();
//public static Stream PtfToPng(string FileInfo)
//{
//byte[] by = Convert.FromBase64String(FileInfo);
//doc.LoadFromBytes(by);
//Image bmp = doc.SaveAsImage(0);//默认第一页
//return ImageToStream(bmp);
或者
//遍历PDF每一页
//for (int i = 0; i < doc.Pages.Count; i++)
//{
// //将PDF页转换成Bitmap图形
// Image bmp = doc.SaveAsImage(i);
// //将Bitmap图形保存为Png格式的图片
// string fileName = string.Format("Page-{0}.png", i + 1);
// bmp.Save(fileName, System.Drawing.Imaging.ImageFormat.Png);
//}
//}

2.

Install-Package PdfiumViewer -Version 2.13.0

Install-Package ImageResizer.Plugins.PdfiumRenderer.Pdfium.Dll -Version 1.0.1

    /// <summary>  
    /// ptf转图片流  
    /// </summary>  
    /// FileInf base64string  
    /// <returns></returns>  
    public static Stream PtfToPng(string FileInfo)  
    {  
        byte\[\] by = Convert.FromBase64String(FileInfo);  
        Stream sm = new MemoryStream(by);  
        using (var document = PdfiumViewer.PdfDocument.Load(sm))  
        {  
            var size = document.PageSizes\[\];  
            Image ig = document.Render(, (int)size.Width, (int)size.Height, , , PdfiumViewer.PdfRenderFlags.Annotations);  
            return ImageToStream(ig);  
        }  
    }

    /// <summary>  
    /// 返回图片流  
    /// </summary>  
    public static Stream ImageToStream(Image img)  
    {  
        MemoryStream ms = new MemoryStream();  
        img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);  
        return ms;  
    }

3.aspose.ptf,最下方有方块，

private Stream ConvertToImage(Stream sm)
{
Document doc = new Document(sm);
if (doc == null)
Console.Write(doc);
MemoryStream stream = new MemoryStream();
Resolution reso = new Resolution();
JpegDevice jpegDevice = new JpegDevice(reso, );
jpegDevice.Process(doc.Pages[], stream);
return stream;
// //Image img = Image.FromStream(stream);
}

4.O2S.Components.PDFRender4NET

///

/// 将PDF文档转换为图片的方法 ///

/// 设置图片的清晰度，数字越大越清晰(1-10)
public static Stream ConvertPdfImage(string Base64, int definition)
{
byte[] by = Convert.FromBase64String(Base64);
Stream sm = new MemoryStream(by);
PDFFile pdfFile = PDFFile.Open(sm);
Bitmap pageImage = pdfFile.GetPageImage(, * definition);
pdfFile.Dispose();
return ImageToStream(pageImage);
}

    /// <summary>  
    /// 返回图片流  
    /// </summary>  
    public static Stream ImageToStream(Image img)  
    {  
        MemoryStream ms = new MemoryStream();  
        img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);  
        return ms;  
    }

无水印的O2S.Components.PDFRender4NET地址https://pan.baidu.com/s/1h8Zb4j4ofUnS4ZBoHJecHQ        码：cum8