title: Using Spire.PDF to merge pdf files Errors
body: <p>I am using the free licenced version of Spire PDF. My program has in the region of 166,ooo pdf files which represent individual pages. I need to merge between 1 and 20 of these with the same names into one pdf.</p>
  
  <p>I have a routine the builds a string of filenames to be added to an array which is passed to the following sub as PDFFiles. The OutputFile is the string with the name of the output file with it's path.</p>
  
  <pre><code>      Private Sub MergePDFs(ByVal PDFFiles As String, ByVal OutPutFile As String)
      Dim files As [String]() = New [String]() {"E:\Ballads of the 20th Century\1st bari #1.pdf", "E:\Ballads of the 20th Century\1st bari #2.pdf"}
      Dim i As Integer
      'open pdf documents            
      Dim docs As PdfDocument() = New PdfDocument(files.Length - 1) {}
      For i = 0 To files.Length - 1
          docs(i) = New PdfDocument(files(i))
      Next
  
      'append document
      docs(0).AppendPage(docs(1))
  
      'import PDF pages
      i = 0
      While i &lt; docs(2).Pages.Count
          docs(0).InsertPage(docs(2), i)
          i = i + 2
      End While
  End Sub
  </code></pre>
  
  <p>I have the Solution  Explorer I have the Spire.Pdf.dll as a file. In References I have Spire.Pdf and Spire.Licence.</p>
  
  <p>At runtime I get An unhandled exception of type 'System.ArgumentException' occurred in Spire.Pdf.dll
  Additional information: File doesn't exist.</p>
  
  <p>The PDFFiles is not used in this example for clarity. The two files listed are taken directly from the program output for testing purposes.</p>
  
  <p>There has to be a simple explanation for this error, but I haven't found one yet.</p>
  
  <p>Please can you help solve it.
  Thanks
  Graham</p>