Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Excel.Range, Cancel As Boolean)
Dim testo As String
Dim nomefile As String
Dim path As String

On Error Resume Next

If Target.Column = 5 Then

    path = "C:UsersAlex"
    testo = path & Cells(Target.Row, 5)
    nomefile = Dir(Left(testo, Len(testo)) & "*.pdf")

    If nomefile = "" Then
        MsgBox "File non trovato", vbCritical, "ATTENZIONE"
        Exit Sub
    End If

    Do
        Shell "C:Program Files (x86)AdobeReader 11.0ReaderAcroRd32.exe " & path & nomefile, vbMaximizedFocus
        nomefile = Dir
    Loop While nomefile <> ""
End If
End Sub

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Excel.Range, Cancel As Boolean)
    Dim testo As String
    Dim FSO As Object
    Dim Folder As Object
    Set FSO = CreateObject("Scripting.FileSystemObject")

    Set Folder = FSO.GetFolder("C:UsersAlex")
    ...
    ...
    testo = path & Cells(Target.Row, 5)
    nomefile = FindFile(testo, Folder, FSO)
End Sub

Function FindFile(FileName As String, Folder As Object, ByRef FSO As Object) As String
    DoEvents

    If FSO.FileExists(Folder & "" & FileName & ".pdf") Then
        FindFile = Folder & "" & FileName & ".pdf"
        Exit Function
    End If

    Dim SubFolder As Object
    For Each SubFolder In Folder.SubFolders
        FindFile = FindFile(FileName, SubFolder, FSO)
    Next
End Function

Function FindFile(FileName As String, Folder As Object, ByRef FSO As Object) As String
DoEvents

If FSO.FileExists(Folder & "" & FileName & "*.pdf*") Then
    FindFile = Folder & "" & FileName & "*.pdf*"
    Exit Function
End If

Dim SubFolder As Object
For Each SubFolder In Folder.SubFolders
    FindFile = FindFile(FileName, SubFolder, FSO)
Next

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Excel.Range, Cancel As Boolean)
Dim testo As String
Dim nomefile As String
Dim FSO As Object
Dim Folder As Object

Set FSO = CreateObject("Scripting.FileSystemObject")
Set Folder = FSO.GetFolder("C:UsersAlex")
If Target.Column = 5 Then
    testo = Cells(Target.Row, 5)
    nomefile = FindFile(testo, Folder, FSO)

    If nomefile = "" Then
        MsgBox "File not found!", vbCritical, "WARNING"
        Exit Sub
    End If

    CreateObject("WScript.Shell").Run nomefile
End If