static extern uint AssocQueryString(AssocF flags, AssocStr str, string pszAssoc, string pszExtra, [Out] StringBuilder pszOut, ref uint pcchOut);

Private Shared Function AssocQueryString(ByVal flags As UInteger, ByVal str As UInteger, ByVal pszAssoc As String, ByVal pszExtra As String, ByVal pszOut As Text.StringBuilder, ByRef pcchOut As UInteger) As UInteger

static string AssocQueryString(AssocStr association, string extension)

  uint ret = AssocQueryString(AssocF.None, association, extension, null, null, ref length);

  ret = AssocQueryString(AssocF.None, association, extension, null, sb, ref length);