The use of the autopen, a device that reproduces signatures and is ubiquitous in government and business, is ordinarily uncontroversial. There is no power to undo a pardon in the Constitution or case law.

Donald Trump says Joe Biden's last-minutes pardons via autopen are null and void. But what is an autopen? And what does it mean for pardons?

The flurry of pardons issued by President Joe Biden in his final days looks poised to face a legal challenge by the Trump administration because of the way he signed them.Legal experts say the law is clear on the use of autopen,