Code:

private void button5_Click(object sender, EventArgs e)
        {            
            ThreadStart threadDelegate = new ThreadStart(ReorderPdfFolder);
            simpleThread = new System.Threading.Thread(threadDelegate);
            simpleThread.IsBackground = true;
            simpleThread.SetApartmentState(ApartmentState.STA);
            simpleThread.Start();
        }

Code:

private void ReorderPdfFolder()
        {            
            string pathToUnsortedFolder = null;
            FolderBrowserDialog fbd = new FolderBrowserDialog();
            fbd.RootFolder = Environment.SpecialFolder.MyComputer;

            if (fbd.ShowDialog() == DialogResult.OK)
            {
                pathToUnsortedFolder = fbd.SelectedPath;
            }

            
            DirectoryInfo dir = new DirectoryInfo(pathToUnsortedFolder);
            FileInfo[] filesInCurrentDirectory = dir.GetFiles();

            PDDocument pdfDocument;
            PDFTextStripper pdfStripper = new PDFTextStripper();

            List<string> completed = new List<string>();

            foreach (FileInfo f in filesInCurrentDirectory)
            {
                try
                {
                    pdfDocument = PDDocument.load(f.FullName);
                    string tempPdfText = pdfStripper.getText(pdfDocument);                   
                    
                    completed.Add(tempPdfText);
                }
                catch (System.Exception)
                {
                    continue;
                }
            }
        }
    }