Retrieve File Association and open a file in its native application

کد:
Private Declare Function FindExecutable Lib "shell32" Alias "FindExecutableA" (ByVal lpFile As String, ByVal lpDirectory As String, ByVal sResult As String) As Long

    Private Const MAX_PATH As Long = 260

    Private Const ERROR_FILE_NO_ASSOCIATION As Long = 31

    Private Const ERROR_FILE_NOT_FOUND As Long = 2

    Private Const ERROR_PATH_NOT_FOUND As Long = 3

    Private Const ERROR_FILE_SUCCESS As Long = 32 'my constant

    Private Const ERROR_BAD_FORMAT As Long = 11

    Dim mflg As Boolean

    Public ActiveClientName As String

    Function retassoc(fn As String, fpath As String) As String

    ' retrieve the associated program that uses this file

    Dim success As Long

    Dim pos As Long

    Dim sResult As String

    sResult = Space$(MAX_PATH)

    success = FindExecutable(fn, fpath, sResult)

    pos = InStr(sResult, Chr$(0))

    If pos Then

    retassoc = Left$(sResult, pos - 1)

    End If

    End Function

    Function LoadUserFile(ByVal FN2Load As String)

    On Error GoTo load_err

    ' load the file in its' native application

    For x = Len(FN2Load) To 0 Step -1

    If Mid(FN2Load, x, 1) = "\" Then

    opPath = Left(FN2Load, x)

    opFile = Right(FN2Load, Len(FN2Load) - x)

    Exit For

    End If

    Next

    Call Shell(retassoc(opFile, opPath) & " " & Chr(34) & FN2Load & Chr(34), vbNormalFocus)

    Exit Function

    load_err:

    MsgBox "The file you are trying to open apparently has no program association available" & vbCrLf & "or it is a corrupted file. I can't open " & opFile, vbInformation + vbOKOnly, "Error occured on file open"

    On Error GoTo 0

    End Function