Hi Amol,
MapiCalendar represent pure calendar items and attachments can be added to MailMessage or MapiMessage only. Please have a look at one of the possible code samples that initializes an Appointment object and adds an attachment to its MailMessage view.
Sample Code:
Appointment appointment = new Appointment(
"Meeting Room 3 at Office Headquarters", // Location
"Monthly Meeting", // Summary
"Please confirm your availability.", // Description
DateTime.Now,
DateTime.Now.AddHours(2),
"from@domain.com", // Organizer
"attendees@domain.com" // Attendees
);
// Save the appointment in ICS format
MemoryStream memStream = new MemoryStream();
appointment.Save(memStream, AppointmentSaveFormat.Ics);
MailMessage mailMsg = new MailMessage();
mailMsg.AddAlternateView(appointment.RequestApointment());
//add the attachment to message
mailMsg.Attachments.Add(new Attachment("About Aspose.pdf"));
MapiMessage mapiMsg = MapiMessage.FromMailMessage(mailMsg);
mapiMsg.Save("TCA2.msg");