需要引用Microsoft.Office.Interop.Word，版本是07之上的。
这个版本会判断文件是否被占用。

using Microsoft.Office.Interop.Word;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
namespace SavePdf
{class Program{private static int NONE_EXIST = -1;private static int OCCUPY = 1;private static int NONE_OCCUPY = 0;[DllImport("kernel32.dll")]public static extern IntPtr _lopen(string lpPathName, int iReadWrite);[DllImport("kernel32.dll")]public static extern bool CloseHandle(IntPtr hObject);public const int OF_READWRITE = 2;public const int OF_SHARE_DENY_NONE = 0x40;public readonly IntPtr HFILE_ERROR = new IntPtr(-1);static void Main(string[] args){Program sp = new Program();foreach (var arg in args){Console.WriteLine(arg);}if (args.Length == 2){if (sp.IsOCcupy(args[0]) == NONE_OCCUPY){DateTime dt = DateTime.Now;sp.SavePdf(args[0], args[1]);TimeSpan ts = DateTime.Now.Subtract(dt);Console.WriteLine(ts.ToString() + "ms");}}}public int IsOCcupy(String vFileName){if (!File.Exists(vFileName)){return NONE_EXIST;}IntPtr vHandle = _lopen(vFileName, OF_READWRITE | OF_SHARE_DENY_NONE);if (vHandle == HFILE_ERROR){return OCCUPY;}CloseHandle(vHandle);return NONE_OCCUPY;}private void SavePdf(String filePath, String outFile){object oMissing = System.Reflection.Missing.Value;_Application wordApp;_Document wordDoc;if (File.Exists(filePath) == false){return;}FileInfo fi = new FileInfo(filePath);object outputFileName = Path.Combine(fi.Directory.FullName, outFile);object fileFormat = WdSaveFormat.wdFormatPDF;wordApp = new Microsoft.Office.Interop.Word.Application();wordApp.Visible = false;object file = (object)filePath;wordDoc = wordApp.Documents.Open(ref file, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing);wordDoc.SaveAs(ref outputFileName, ref fileFormat, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing, ref oMissing);try{if (wordDoc != null){wordDoc.Close(ref oMissing, ref oMissing, ref oMissing);}if (wordApp != null){wordApp.Quit(ref oMissing, ref oMissing, ref oMissing);}}catch (Exception ex){throw ex;}return;}}
}