Sub Open_CheckedCCs_Click()
Dim aCC As ContentControl, xlApp As Object, xlWkBk As Object
  Dim sPath As String, sFullPath As String
    sPath = "C:\Temp\MyDocs\"    'xl files in fixed location
  On Error Resume Next
    Set xlApp = GetObject(, "Excel.Application")
  On Error GoTo 0
  For Each aCC In ActiveDocument.Range.ContentControls
    If aCC.Type = wdContentControlCheckBox Then
      sFullPath = sPath & aCC.Tag
      If aCC.Checked And fFileExists(sFullPath) Then
        If xlApp Is Nothing Then Set xlApp = CreateObject("Excel.Application")
        Set xlWkBk = xlApp.Workbooks.Open(sFullPath)
        xlApp.Visible = True
        xlWkBk.Activate
      End If
    End If
  Next aCC
  
End Sub

Function fFileExists(sPath As String) As Boolean
  Dim fso As Object
  Set fso = CreateObject("Scripting.FileSystemObject")
  fFileExists = fso.FileExists(sPath)
End Function