summing quantity for each duplicate item across files

Hasson

In the attached revised file (name changed), I've modified your macro as shown in bold below (with comments you can remove). It needs to be run in a folder containing your other files (however many).

I've added some variables to reduce the code but essentially it now:

1. clears the results in sheet RP
2. adds the quatiities from column E of the other files (into column C)
3. removes your line using the (Range) .RemoveDuplicates method and
4. sorts the results, applies subtotals (then collapses them to show only the totals) before
5. using a simple loop to number the (visible) subtotal items.

It says things like "Item 1" since you can use the Subtotal controls to show the (level 3) detail i.e. which item a quantity was in another file. 

Sub PullData()
    Dim MyObj As Object, MySource As Object, file As Variant
    Dim wb As Workbook, wbMe As Workbook
    Dim ws As Worksheet, wsMe As Worksheet
    Dim Path As String
    Dim wsLstRw As Long, wsLstSub As Long, n as Long

    Path = ThisWorkbook.Path & "\"
    file = Dir(Path)

    Set wbMe = ThisWorkbook: Set wsMe = wbMe.Sheets("RP")

    'clear existing results
    wsMe.Range("A2").CurrentRegion.Offset(1, 0).EntireRow.Delete

    While (file <> "" And LCase(file) <> "result.xlsm") ' ### changed file name
        Set wb = Workbooks.Open(Path & file): Set ws = wb.Sheets(1)
        'get last item in A
        wsLstRw = ws.Range("A" & Rows.Count).End(xlUp).Row
        ws.Range("A2:B" & wsLstRw).Copy wsMe.Range("A" & wsMe.Range("A" & Rows.Count).End(xlUp).Row + 1)
        'also copy quantities to column C
        ws.Range("E2:E" & wsLstRw).Copy wsMe.Range("C" & wsMe.Range("C" & Rows.Count).End(xlUp).Row + 1)
        wb.Close False
        file = Dir
    Wend

    'sort values in B
    wsMe.Range("A:C").Sort Key1:=wsMe.Range("B2"), Order1:=xlAscending, Header:=xlYes
    ' add sub-totals to C when B changes
    wsMe.Range("A2").CurrentRegion.Subtotal GroupBy:=2, Function:=xlSum, TotalList:=3
    'collapse to show subtotals only
    wsMe.Outline.ShowLevels RowLevels:=2
    'get row
    wsLstSub = wsMe.Range("C" & Rows.Count).End(xlUp).Row
    ' loop through visible cells and add text + number
    For Each Cl In Range("A2:A" & wsLstSub - 1).SpecialCells(xlCellTypeVisible)
        n = n + 1
        Cl.Value = "Item " & n
    Next Cl

End Sub

If you don't want to use subtotals, the second file has slightly different code and uses   a loop (running backwards from the last data row to row and deleting matching rows after summing data). Heres' just that code segment (after the Wend line) with comments:

    'sort values in B
    wsMe.Range("A:C").Sort Key1:=wsMe.Range("B2"), Order1:=xlAscending, Header:=xlYes
    ' loop backwards,  adding numbers if B matches
    For n = wsMe.Range("C" & Rows.Count).End(xlUp).Row To 3 Step -1
        'Look at value in B and if matching row above, add quantity to row above and delete row
        With wsMe.Cells(n, 2)
            If .Value = .Offset(-1, 0).Value Then
                .Offset(-1, 1).Value = .Offset(-1, 1).Value + .Offset(0, 1).Value
                .EntireRow.Delete
            End If
        End With
    Next n
    ' renumber items
    wsMe.Range("A2") = 1: wsMe.Range("A2").AutoFill Destination:=wsMe.Range("A2:A" & wsMe.Range("A" & Rows.Count).End(xlUp).Row), Type:=xlFillSeries

End Sub

While (file <> "" And LCase(file) <> "result via loop.xlsm") ' ### changed file name

Hope this makes sense and helps.