C# Convert PDF to Image

图片转换需要安装：https://ghostscript.com/

引入：

<ItemGroup>
    <PackageReference Include="Magick.NET-Q16-AnyCPU" Version="13.4.0" />
    <PackageReference Include="Microsoft.IO.RecyclableMemoryStream" Version="2.3.2" />
</ItemGroup>

定义转换配置：

public class PdfConvertSetting
{
    /// <summary>
    /// PDF 文件位置
    /// </summary>
    public string SourcePdfPath { get; init; }

    /// <summary>
    /// 分辨率，默认打印机 dpi 96
    /// </summary>
    public int Dpi { get; set; } = 300;

    /// <summary>
    /// 将 pdf 转为为何种类型
    /// </summary>
    public MagickFormat ImageType { get; set; } = ImageType.PNG;

    /// <summary>
    /// PDF 纸张大小
    /// </summary>
    public PageSizeType PageSize { get; set; } = PageSizeType.A4;
}

然后根据文件，自动将每页 pdf 转为图片，然后将图片合并到 pdf 中。

/// <summary>
/// 将 pdf 打印为图片 pdf
/// <param name="setting"></param>
/// <returns></returns>
public static async Task<string> PdfToPdf(PdfConvertSetting setting)
{
    var imageExtension = ".png";  // 根据情况配置
    var ticks = DateTime.Now.Ticks.ToString();
    var imagesPath = Path.Combine("temp", DateTime.Now.Ticks.ToString());
    Directory.CreateDirectory(imagesPath);

    FileInfo fileInfo = new FileInfo(setting.SourcePdfPath);

    var settings = new MagickReadSettings
    {
        Density = new Density(setting.Dpi, setting.Dpi)
    };

    using var oldPdf = new MagickImageCollection();
    using var newPdf = new MagickImageCollection();

    oldPdf.Read(fileInfo, settings);

    int pageIndex = 0;
    foreach (var image in oldPdf)
    {
        image.Format = setting.ImageType;
        var fileName = Path.Combine(imagesPath, pageIndex.ToString() + imageExtension);
        await image.WriteAsync(fileName);
        newPdf.Add(new MagickImage(fileName));
        pageIndex++;
    }
    oldPdf.Dispose();
    var filename = Path.Combine(imagesPath, ticks + ".pdf");
    newPdf.Write(filename);
    return filename;
}

将整个 pdf 合成一张图片：

/// <summary>
/// 整个 pdf 文件转为图片
/// </summary>
/// <param name="sourcePath"></param>
/// <param name="dpi"></param>
/// <param name="y">是否 y 轴拼接，可以选择↓→两种拼接方向</param>
/// <returns></returns>
public static async Task<string> PdfToImage(string sourcePath, int dpi = 300, bool y = false)
{
    var ticks = DateTime.Now.Ticks.ToString();
    var imagesPath = Path.Combine(Constants.CurrentTempDir, DateTime.Now.Ticks.ToString());
    Directory.CreateDirectory(imagesPath);
    var imageFile = Path.Combine(imagesPath, ticks + ".png");
    var settings = new MagickReadSettings
    {
        Density = new Density(dpi)
    };

    using var images = new MagickImageCollection();
    images.Read(sourcePath, settings);

    if (y == true)
    {
        using var horizontal = images.AppendHorizontally();
        horizontal.Format = MagickFormat.Png;
        await horizontal.WriteAsync(imageFile);
    }
    else
    {
        using var vertical = images.AppendVertically();
        vertical.Format = MagickFormat.Png;
        await vertical.WriteAsync(imageFile);
    }

    return imageFile;
}