private void MergePDFFiles(string[] fileList, string outMergeFile)  
        {  
            List<PdfReader> readerList = new List<PdfReader>();//記錄合並PDF集合  
            iTextSharp.text.Document document = new iTextSharp.text.Document(iTextSharp.text.PageSize.A4.Rotate());  
            PdfWriter writer = PdfWriter.GetInstance(document, new FileStream(outMergeFile, FileMode.Create));  
            document.Open();  
  
            PdfContentByte cb = writer.DirectContent;  
            PdfImportedPage newPage;  
            for (int i = 0; i < fileList.Length; i++)  
            {  
                if (!string.IsNullOrEmpty(fileList[i]))  
                {  
                    PdfReader reader = new PdfReader(fileList[i]);  
                    int iPageNum = reader.NumberOfPages;  
                    for (int j = 1; j <= iPageNum; j++)  
                    {  
                        document.NewPage();  
                        newPage = writer.GetImportedPage(reader, j);  
                        cb.AddTemplate(newPage, 0, 0);  
                    }  
                    readerList.Add(reader);  
                }  
            }  
            document.Close(); 

1             foreach (var rd in readerList)  
2             {  
3                 rd.Dispose();  
4             }  

原文鏈接：http://blog.csdn.net/hebbers/article/details/70332015 關鍵點在與

PdfReader的循環釋放，定義局部變量後獨立釋放引用並不能完全釋放，需要單獨循環釋放。

  List<PdfReader> readerList = new List<PdfReader>(); 
 

    foreach (var rd in readerList)  
             {  
               rd.Dispose();  
             }  

iTextSharp 合並PDF後，無法刪除已經合並的單個文件