public static string MergePDFFiles(List <string> filesPaths) { Spire.Pdf.PdfDocument[] tickets = new Spire.Pdf.PdfDocument[filesPaths.Count()]; for (int i = 0; i < tickets.Length; i++) { tickets[i] = new Spire.Pdf.PdfDocument(filesPaths[i]); } Spire.Pdf.PdfDocument document = new Spire.Pdf.PdfDocument(); for (int i = 0; i < tickets.Length; i++) { document.InsertPage(tickets[i], 0); } string now = DateTime.Now.ToString("yyyy/MM/dd_HH.mm.ss.fff"); document.SaveToFile(@"D:\Virtuace\HW6\Booking\Booking\Tickets\" + now + ".pdf"); return(@"D:\Virtuace\HW6\Booking\Booking\Tickets\" + now + ".pdf"); }