PM> Install-Package Spire.PDF

using Spire.Pdf;
using Spire.Pdf.Graphics;
using System.Drawing;
using System.IO;

namespace ConvertMultipleImagesIntoPdf
{
    class Program
    {
        static void Main(string[] args)
        {
            //创建PdfDocument对象
            PdfDocument doc = new PdfDocument();

            //将页边距设置为零
            doc.PageSettings.SetMargins(0);

            //获取存储图像的文件夹
            DirectoryInfo folder = new DirectoryInfo(@"C:\Users\Administrator\Desktop\图片");

            //遍历文件夹中的文件
            foreach (FileInfo file in folder.GetFiles())
            {
                //加载特定图像
                Image image = Image.FromFile(file.FullName);

                //获取图像宽度和高度
                float width = image.PhysicalDimension.Width;
                float height = image.PhysicalDimension.Height;

                //添加与图像大小相同的页面
                PdfPageBase page = doc.Pages.Add(new SizeF(width, height));

                //基于图像创建PdfImage对象
                PdfImage pdfImage = PdfImage.FromImage(image);

                //在页面的（0，0）处绘制图像
                page.Canvas.DrawImage(pdfImage, 0, 0, pdfImage.Width, pdfImage.Height);
            }

            //保存文件
            doc.SaveToFile("结果文档.pdf");
            doc.Dispose();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports System.Drawing
Imports System.IO

Namespace ConvertMultipleImagesIntoPdf
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            '创建PdfDocument对象
            Dim doc As PdfDocument = New PdfDocument()

            '将页边距设置为零
            doc.PageSettings.SetMargins(0)

            '获取存储图像的文件夹
            Dim folder As DirectoryInfo = New DirectoryInfo("C:\Users\Administrator\Desktop\图片")

            '遍历文件夹中的文件
            For Each file In folder.GetFiles()
                '加载特定图像
                Dim image As Image = Image.FromFile(file.FullName)

                '获取图像宽度和高度
                Dim width As Single = image.PhysicalDimension.Width
                Dim height As Single = image.PhysicalDimension.Height

                '添加与图像大小相同的页面
                Dim page As PdfPageBase = doc.Pages.Add(New SizeF(width, height))

                '基于图像创建PdfImage对象
                Dim pdfImage As PdfImage = PdfImage.FromImage(image)

                '在页面的（0，0）处绘制图像
                page.Canvas.DrawImage(pdfImage, 0, 0, pdfImage.Width, pdfImage.Height)
            Next

            '保存文件
            doc.SaveToFile("结果文档.pdf")
            doc.Dispose()
        End Sub
    End Class
End Namespace