Why won't this VBA code loop through?

Question

I am trying to get it to print the files from folder in C2, which it does, and then go on to repeat for C3. It works fine the first time I run it, but when it tries for C3, it outputs the error sequence that it can't insert the pages, and then cannot save and there is no output file. My basic understand of VBA makes me think one of the integers or the array isn't 'resetting'.

What do you think? How can I fix so it'll loop through a few different folders to output.

    Sub MergePDFs()

    Dim a() As String, i As Long, n As Long, ni As Long, p As String, f As String
    Dim AcroApp As New Acrobat.AcroApp, PartDocs() As Acrobat.CAcroPDDoc
    Dim DestFile As String '<-- change to suit
    Dim t As Integer
    Dim MyPath As String, MyFiles As String

     ' Choose the folder or just replace that part by: MyPath = Range("E3")
         '.InitialFileName = "C:\Temp\"
    For t = 0 To 1
    MyPath = Cells(t + 2, 3).Value
     DestFile = Cells(t + 2, 1).Value & ".pdf"

     ' Populate the array a() by PDF file names
    If Right(MyPath, 1) <> "\" Then MyPath = MyPath & "\"
    ReDim a(1 To 2 ^ 14)
    f = Dir(MyPath & "*.pdf")
    While Len(f)
        If StrComp(f, DestFile, vbTextCompare) Then
            i = i + 1
            a(i) = f
        End If
        f = Dir()
    Wend

     ' Merge PDFs
    If i Then
        ReDim Preserve a(1 To i)
        MyFiles = Join(a, ",")
        Application.StatusBar = "Merging, please wait ..."
        Application.StatusBar = False


    If Right(MyPath, 1) = "\" Then p = MyPath Else p = MyPath & "\"
    a = Split(MyFiles, ",")
    ReDim PartDocs(0 To UBound(a))

    On Error GoTo exit_
    If Len(Dir(p & DestFile)) Then Kill p & DestFile
    For i = 0 To UBound(a)
         ' Check PDF file presence
        If Dir(p & Trim(a(i))) = "" Then
            MsgBox "File not found" & vbLf & p & a(i), vbExclamation, "Canceled"
            Exit For
        End If
         ' Open PDF document
        Set PartDocs(i) = CreateObject("AcroExch.PDDoc")
        PartDocs(i).Open p & Trim(a(i))
        If i Then
             ' Merge PDF to PartDocs(0) document
            ni = PartDocs(i).GetNumPages()
            If Not PartDocs(0).InsertPages(n - 1, PartDocs(i), 0, ni, True) Then
                MsgBox "Cannot insert pages of" & vbLf & p & a(i), vbExclamation, "Canceled"
            End If
             ' Calc the number of pages in the merged document
            n = n + ni
             ' Release the memory
            PartDocs(i).Close
            Set PartDocs(i) = Nothing
        Else
             ' Calc the number of pages in PartDocs(0) document
            n = PartDocs(0).GetNumPages()
        End If
    Next

    If i > UBound(a) Then
         ' Save the merged document to DestFile
        If Not PartDocs(0).Save(PDSaveFull, p & DestFile) Then
            MsgBox "Cannot save the resulting document" & vbLf & p & DestFile, vbExclamation, "Canceled"
        End If
    End If

exit_:

     ' Inform about error/success
    If Err Then
        MsgBox Err.Description, vbCritical, "Error #" & Err.Number
    ElseIf i > UBound(a) Then
        MsgBox "The resulting file is created:" & vbLf & p & DestFile, vbInformation, "Done"
    End If

     ' Release the memory
    If Not PartDocs(0) Is Nothing Then PartDocs(0).Close
    Set PartDocs(0) = Nothing

     ' Quit Acrobat application
    AcroApp.Exit
    Set AcroApp = Nothing
    Else
        MsgBox "No PDF files found in" & vbLf & MyPath, vbExclamation, "Canceled"
    End If
    Next t
End Sub

Answer 1

After the start of your For t loop, reset the value of i:

For t = 0 To 1
    i = 0

If you currently have 5 files in the first directory, the files from the second directory will currently be placed in positions 6+ of your array, with the first five positions being set to blanks. That will undoubtedly cause problems later when you try to access those "blank" filenames.

By resetting your counter, the new filenames will be placed in positions 1+ of your array.