Make a backup copy of the calendar
If you want to take a snapshot of your calendar, you can make a backup copy, which is just a picture of your calendar at that point in time. You won’t be able to schedule new events to this backup copy of your calendar after you restore it.
Note If you’re using an email account at work, you probably have an Exchange account, which means Outlook items, including your calendar, are already automatically backed up periodically.
To create a local backup of your calendar, you can export it to a .pst file.
Click File > Open & Export > Import/Export.
Click Export to a file, and then click Next.
Click Outlook Data File (.pst), and click Next.
Click Calendar and then click Next.
Pick a location and name for your backup file, and then click Finish.
If you want to ensure no one has access to your files, enter and confirm a password, and then click OK.
To restore the backed up Outlook items from the .pst, just import the file to Outlook. Just remember that if you restore your backup copy, you won’t be able to schedule new items. You’ll only be able to view the snapshot of your calendar.