问我使用iText 7将多个PDF合并到一个使用c#的文件夹中。在我把它们合并后，它们似乎都留在了记忆中。我怎么才能把他们清除出去？

EN

private void button1_Click(object sender, EventArgs e)
        {
            folderBrowserDialog1 = new FolderBrowserDialog();
            DialogResult = folderBrowserDialog1.ShowDialog();

            if(DialogResult == DialogResult.OK)
            {
                textBox1.Text = folderBrowserDialog1.SelectedPath;
                Environment.SpecialFolder root = folderBrowserDialog1.RootFolder;
            }


            if(folderBrowserDialog1.SelectedPath != "")
            {
                
                IList<string> inputFiles = Directory.GetFiles(folderBrowserDialog1.SelectedPath);

                //destination to make merged file
                string dest = @"D:\PDF-merge";
                string filename = "merged.pdf";

                try
                {
                    System.IO.Directory.CreateDirectory(dest);
                }
                catch { }


                //creating merge file
                PdfDocument pdfDoc = new PdfDocument(new PdfWriter(dest + @"\" + filename));
                PdfMerger merger = new PdfMerger(pdfDoc);
                
                PdfReader reader;
                PdfDocument pdf2merge;

                
                for (int i = 0; i < inputFiles.Count; i++)
                {
                    if (Path.GetExtension(inputFiles[i]) == ".pdf")
                    {
                        reader = new PdfReader(inputFiles[i]);
                        reader.SetUnethicalReading(true);
                        pdf2merge = new PdfDocument(reader);
                        merger.Merge(pdf2merge, 1, pdf2merge.GetNumberOfPages());

                        reader.Close();
                        pdf2merge.Close();
                    }
                }
                
                merger.Close();
                
            }
        }