What is the most logical next event?

How to secretly open a sealed envelope
Place a tea kettle on the stove.
Boil water in a tea kettle until steam begins to shoot through the spout. The steam is what you'll use to loosen the glue in the envelope you want to open.
Keep in mind that the steam method can get a little messy and potentially warp the paper, so if it's imperative that the envelope looks fresh and new, you might want to just use a new envelope instead. If the steam is coming out in a strong, steady stream, stick a spoon in the spout to diffuse it.