All unlicensed copies of Flying Logic revert to Reader Mode.
If you only want to open, read, and explore Flying Logic documents sent to you by others, or open documents you created in the past without a subscription, you can simply let the trial period expire, and then Flying Logic will be in Reader Mode.
In Reader Mode you can open Flying Logic documents, scroll through them, change display modes, collapse and uncollapse groups, and change confidence spinners and even export or print the document. But any attempts to actually modify or save the document will be met with a friendly reminder to purchase a license for the whole product.