Macro/VBA to merge to documents

ShadowHawk26 

Maybe this VBA approach will help you, if not please just ignore it.

Sub MergeFiles()
    Dim wsParent As Worksheet
    Dim wsDonor As Worksheet
    Dim lastRowParent As Long, lastRowDonor As Long
    Dim i As Long, j As Long, insertRow As Long
    Dim donorCriteria1 As Variant, donorCriteria2 As Variant, donorCriteria3 As Variant
    Dim donorInfo1 As Variant, donorInfo2 As Variant
    Dim parentCriteria1 As Variant, parentCriteria2 As Variant, parentCriteria3 As Variant
    
    ' Set references to the worksheets
    Set wsParent = ThisWorkbook.Sheets("ParentSheetName") ' Adjust the sheet name as necessary
    Workbooks.Open "C:\path\to\DonorFile.xlsx" ' Change to the actual path of the donor file
    Set wsDonor = Workbooks("DonorFile.xlsx").Sheets("DonorSheetName") ' Adjust the sheet name as necessary
    
    ' Find the last rows in both sheets
    lastRowParent = wsParent.Cells(wsParent.Rows.Count, "A").End(xlUp).Row
    lastRowDonor = wsDonor.Cells(wsDonor.Rows.Count, "A").End(xlUp).Row
    
    ' Loop through each row in the parent file
    For i = 2 To lastRowParent ' Assuming headers in the first row
        parentCriteria1 = wsParent.Cells(i, "A").Value
        parentCriteria2 = wsParent.Cells(i, "B").Value
        parentCriteria3 = wsParent.Cells(i, "C").Value
        
        ' Loop through the donor file to find matching rows
        For j = 2 To lastRowDonor
            donorCriteria1 = wsDonor.Cells(j, "A").Value
            donorCriteria2 = wsDonor.Cells(j, "B").Value
            donorCriteria3 = wsDonor.Cells(j, "C").Value
            
            If parentCriteria1 = donorCriteria1 And parentCriteria2 = donorCriteria2 And parentCriteria3 = donorCriteria3 Then
                ' Insert a new row in the parent file
                insertRow = i + 1
                wsParent.Rows(insertRow).Insert Shift:=xlDown
                
                ' Copy data from donor to the new row in parent
                donorInfo1 = wsDonor.Cells(j, "D").Value
                donorInfo2 = wsDonor.Cells(j, "E").Value
                
                wsParent.Cells(insertRow, "A").Value = parentCriteria1
                wsParent.Cells(insertRow, "B").Value = parentCriteria2
                wsParent.Cells(insertRow, "C").Value = parentCriteria3
                wsParent.Cells(insertRow, "D").Value = donorInfo1
                wsParent.Cells(insertRow, "E").Value = donorInfo2
                
                ' Adjust last row of parent as a new row was inserted
                lastRowParent = lastRowParent + 1
                
                ' Move to the next row in the parent file after insertion
                i = i + 1
            End If
        Next j
    Next i
    
    ' Close the donor file without saving
    Workbooks("DonorFile.xlsx").Close SaveChanges:=False
    
    MsgBox "Merging Completed!"
End Sub

VBA code is untested backup your file first.

My answers are voluntary and without guarantee!

Hope this will help you.