让PDF只能被指定的电脑打开

在模块中加入下列声明：
Public Declare Function GetVolumeInformation Lib "kernel32" _
Alias "GetVolumeInformationA" (ByVal lpRootPathName As String, _
ByVal lpVolumeNameBuffer As String, ByVal nVolumeNameSize As Long, _
lpVolumeSerialNumber As Long, lpMaximumComponentLength As Long, _
lpFileSystemFlags As Long, ByVal lpFileSystemNameBuffer As String, _
ByVal nFileSystemNameSize As Long) As Long
'得到某一磁盘分区的信息，如C：

窗体代码如下：
Option Explicit
Private Regid, Localid As Long

Private Sub CmdLocalID_Click()
'根据C盘序列号得到原ID
Dim Driver, VolName, Fsys As String
Dim volNumber, MCM, FSF As Long
Driver = "c:\"
Dim res As Long
res = GetVolumeInformation(Driver, VolName, 127, volNumber, MCM, FSF, Fsys, 127)
'volNumber是C盘序列号
Localid = volNumber / 2 + 123456789
Text1.Text = Localid
End Sub

Private Sub Cm