As Dave indicated, you cannot read the password from the ID file.
But what you can do is change a setting in the Notes client. This setting has been available in Notes for at least 15 years, but the location and wording has changed in different versions. In Notes 8.5, the setting is located in the User Security dialog. It is a checkbox with the label "Don't prompt for password from other Notes-based programs (reduces security)".
If you turn on this setting, and your users are already running the Notes client, they will not have to enter the password again for your macro. But there is a good reason the setting has the warning "(reduces security)" in the label: it means that Notes will allow all programs that use the Notes API to gain access without re-typing the password. With this setting turned off, any virus that tries to use the Notes API to read data (for example, the email address of user's contacts) will get a password prompt -- and well-trained users should recognize that something bad is happening and have the opportunity to stop the virus. If the setting is turned on, users lose this protection. You will have to balance this risk against the benefit of avoiding having to type the password.
Lotus Notes password (Rudy Tjen 25.Jan.12)
Feedback response number WEBB8QURV3 created by Rich Schwartz on 01/25/2012
. . The ID file password is the passwor... (Dave Kern 25.Jan.12)
. . There is a setting that may help yo... (Rich Schwartz 25.Jan.12)
. . . . Which can be set through a policy (Christian Gravg... 1.Feb.12)
. . but have you considered to to deliv... (Peter Rosenberg... 26.Jan.12)