What does the 'Mark as Done' button do?
If you enrol a worker in a pension, your pension company needs to be told about this event. When you create a pension file, the enrolment information is included in the file. Once the file has been accepted by the pension company, you should click 'Mark as Done'.
The 'Mark as Done' button sets the 'Enrolment Complete' option on the 'Pensions etc' tab of each employee whose enrolment details are in the file. You can change the 'Enrolment Complete' setting manually if you prefer. Once it has been set, the enrolment details won't be included in future pension files (unless you change it back to 'No').
Similarly, if a worker leaves a pension, the exit event is included in the pension export file. In this case the 'Mark as Done' button sets the 'Exit Complete' option on the 'Pensions etc' tab.