Actually, you can do this with 15 lines of code and process only one line at a time to eliminate any memory concerns. I've added comments to explain it as it goes.


Code:
    Dim InputFileNum As Integer
    Dim OutputFileNum As Integer
    Dim Buffer As String
    
    ' Get the input file handle and open for input-only
    InputFileNum = FreeFile
    Open "SourceFile.txt" For Input As InputFileNum
    
    ' Get the output file handle and open/create the file
    OutputFileNum = FreeFile
    Open "OutputFile.txt" For Output As OutputFileNum
    
    ' Read each line in the input file one line at a time
    While Not EOF(InputFileNum)
        
        ' Reads one line of text
        Line Input #InputFileNum, Buffer
        
        ' Check to see if MAMPLASAN is contained in that line...this is NOT case sensitive
        ' Use vbBinaryCompare if you are looking for case sensitive
        If (InStr(1, Buffer, "MAMPLASAN", vbTextCompare) <> 0) Then
            ' If it is found, output it to the destination file
            Print #OutputFileNum, Buffer
        End If
    Wend

    Close #OutputFileNum
    Close #InputFileNum