If the file you received has an expiry or a self-destruct timer, that means you have been granted access to the file for a limited time only.
You may access the file as many times you wish during the allotted time. Once the timer has lapsed, you will no longer be able to access the file.
If you wish to access the file after it has expired or self-destructed, please contact the file owner/sender.
How to know if a file has an expiry or self-destruct timer
To see if a file has an expiry or a self-destruct timer, check the bottom-right-hand corner when in the file viewer.
If the file has an expiry date, you'll see the expiry date.
If the file has a self-destruct timer, you'll see the self-destruct timer.