C# 将多个office文件转换及合并为一个PDF文件

private void btnAdd_Click(object sender, EventArgs e)
{
    OpenFileDialog ofd = new OpenFileDialog();
    ofd.Filter = "All files (*.docx, *.pdf, *.pptx, *.pdf)|*.docx;*.pdf;*.pptx;*.xlsx";
    ofd.Multiselect=true;
    if (DialogResult.OK == ofd.ShowDialog())
    {
        string[] files = ofd.FileNames;
        listBox1.Items.AddRange(files);
    }
}

using System.Drawing;
using System.Windows.Forms;
using Spire.Pdf;
using Spire.Doc;
using Spire.Xls;
using Spire.Presentation;
using System.IO;
using Spire.Pdf.Graphics;

namespace ConvertAndMerge
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            PdfFiles = new List();
        }
        public List PdfFiles { get; set;}

        //添加文件到 listbox
        private void btnAdd_Click(object sender, EventArgs e)
        {
            OpenFileDialog ofd = new OpenFileDialog();
            ofd.Filter = "All files (*.docx, *.pdf, *.pptx, *.pdf)|*.docx;*.pdf;*.pptx;*.xlsx";
            ofd.Multiselect=true;
            if (DialogResult.OK == ofd.ShowDialog())
            {
                string[] files = ofd.FileNames;
                listBox1.Items.AddRange(files);
            }
        }

        private void btnMerge_Click(object sender, EventArgs e)
        {
            //将其他格式的文件转换为PDF文件
            string ext=string.Empty;
            foreach (object item in listBox1.Items)
            {
                ext=Path.GetExtension(item.ToString());
                switch (ext)
                {
                    case ".docx":
                        using (MemoryStream ms = new MemoryStream())
                        {
                            Document doc = new Document(item.ToString());
                            doc.SaveToStream(ms, Spire.Doc.FileFormat.PDF);
                            PdfFiles.Add(new PdfDocument(ms));
                        }
                        break;
                    case ".pdf":
                        PdfFiles.Add(new PdfDocument(item.ToString()));
                        break;
                    case ".pptx":
                        using (MemoryStream ms = new MemoryStream())
                        {
                            Presentation ppt = new Presentation(item.ToString(),Spire.Presentation.FileFormat.Auto);
                            ppt.SaveToFile(ms,Spire.Presentation.FileFormat.PDF);
                            PdfFiles.Add(new PdfDocument(ms));
                        }
                        break;
                    case ".xlsx":
                        using (MemoryStream ms = new MemoryStream())
                        {
                            Workbook xls = new Workbook();
                            xls.LoadFromFile(item.ToString());
                            xls.SaveToStream(ms, Spire.Xls.FileFormat.PDF);
                            PdfFiles.Add(new PdfDocument(ms));
                        }
                        break;
                    default:
                        break;
                }              
            }
            //将多个PDF文件合并为一个PDF文件
            PdfDocument newPdf1 = new PdfDocument();
            foreach (PdfDocument doc in PdfFiles)
            {
                newPdf1.AppendPage(doc);
            }
            //创建一个新的、页面大小固定的PDF文件，复制合并文件的内容到该新的PDF文件
            PdfDocument newPdf2 = new PdfDocument();
            foreach (PdfPageBase page in newPdf1.Pages)
            {
                PdfPageBase newPage = newPdf2.Pages.Add(PdfPageSize.A4, new PdfMargins(0));
                PdfTextLayout loLayout = new PdfTextLayout();
                loLayout.Layout = PdfLayoutType.OnePage;
                page.CreateTemplate().Draw(newPage, new PointF(0, 0), loLayout);
            }
            //保存目标PDF文件
            SaveFileDialog sfd = new SaveFileDialog();
            sfd.Filter = "Pdf files(*.pdf)|*.pdf";
            if (DialogResult.OK == sfd.ShowDialog())
            {
                newPdf2.SaveToFile(sfd.FileName);
            }
        }
    }
}