Is it possible to steal the Declaration of Independence?

Answer 1

The original document is secure like you wouldn't believe. And what would anyone do with such a document? Certainly could not sell it. So it is pointless to even think about it.

Observation

A determined individual with unlimited resources might be able to do it. Might. But would require help (an army, perhaps) and the expenditure of a large fortune to even have a chanceof pulling this off. It's probably not impossible, but the probability of success (even with mega$ and manpower at the level or a military division) approaches zero very, very closely. It is probably so difficult as to be considered impossible for all practical purposes. As pointed out, why bother?

Possible but Not Recommended

The original (signed) document is well protected, much more so than is shown in fiction, notably the film National Treasure(2004). The Declaration is in a sealed glass case to protect it from UV radiation and oxygen in the air, and has faded considerably after 230 years.

There are monomaniacal collectors who might attempt its theft, merely for some perverse sense of accomplishment. But they could scarcely profit financially from such a dangerous and expensive criminal act. Its repository is guarded around the clock and few persons even have access to its storage.