one is an empty PdfDocument, your
two is an empty PdfDocument, the for loop does nothing, and outPdf is an empty PdfDocument.
As always, the computer does what you tell him to do. You can easily see that if you step through your code in a Debugger.
You have to use something like
PdfDocument inputDocument = PdfReader.Open(file, PdfDocumentOpenMode.Import); to open a PDF file for import.
new PdfDocument("1.pdf"); does not open/read a file, it just prepares the creation of a new file with that name.