Tienes varias formas de hacerlo, esta es una:
Public Function FileToString(FileName As String) As String
On Error GoTo ErrorHandler
Dim hlngFile As Long, strFile As String
hlngFile = FreeFile
Open FileName For Binary Access Read As hlngFile
FileToString = vbNullString
strFile = String(FileLen(FileName), " ")
Get hlngFile, , strFile
Close hlngFile
FileToString = strFile
Exit Function
ErrorHandler:
FileToString = Empty
End Function
