A document obtained by The Post outlines the narrow set of circumstances in which Trump’s signature can be affixed to documents, following controversy this week kicked off by a Heritage Foundation analysis of Biden signatures on various records, including last-minute pardons.

A small group of officials under both Biden and Trump have been delegated the power to get documents “signed” robotically, but 82-year-old Biden’s perceived cognitive decline has sparked debate about whether some aides may have assumed his wishes in his final stretch as commander-in-chief.

One Biden White House source told The Post they suspect that a key aide to the then-president may have made unilateral determinations on what to auto-sign. The Post is not publishing that staffer’s name due to the lack of concrete evidence and refutations by other colleagues.

The Biden aide, who did not respond to requests for comment, would frequently make mention of what “the boss” wanted, the source said, but compatriots would have “no idea” if it was true because the internal culture was to not ask questions.

“I feared no one as much as I feared that [staffer]. To me, [the staffer] basically was the president,” the person said. “No one ever questioned [the staffer]. Period.”

“Everyone” was suspicious of this individual exceeding their authority when claiming to speak for the president, the source said. “But no one would actually say it.”

“I think [the aide] was using the auto pen as standard and past protocol,” The Post’s informant said.

“There is no clarity on who actually approved what — POTUS or [the aide].”

Several other former staffers, including those who have in the past offered unvarnished assessments of what they view as the shortcomings of the ex-president and his core staff, described the allegation as absurd and said that they never saw the person abuse their authority.

One of the skeptics noted that Biden frequently would “demand to see the most mundane statements” put out by the press office during their tenure early in his term of office — with another calling the entire storyline “bullshit” and that it was “embarrassing” for Trump and his allies to be making it an issue.

Attorney Mike Davis, a prominent outside adviser to Trump and his team, told The Post that the particular circumstances of autopen use matter, noting that it’s common practice in Washington for politicians to delegate auto-signatures to aides.

“If they’re carrying out the president’s will, it doesn’t seem like an issue. If they’re not carrying out the president’s will, it’s a huge issue — it’s criminal,” Davis said, listing forgery, obstruction of justice and fraud as potential charges.

“If an authorized autopen operator is using the autopen on a particular document against the president’s will it’s clearly not valid.”

“If they’re carrying out the president’s will, it doesn’t seem like an issue. If they’re not carrying out the president’s will, it’s a huge issue — it’s criminal,” Davis said, listing forgery, obstruction of justice and fraud as potential charges.

An internal memo drafted Thursday by Trump staff secretary William Scharf, who has for the past two months publicly described and presented documents to Trump for his signature in the Oval Office, lays out the restrictive current use of the autopen.

“We have gone significantly further than [the] need for express approval, both in this Administration and in the First Trump Administration,” Scharf wrote.

“Our practice around autopen usage is far more restrictive than most previous administrations. We do not use the autopen for documents that exercise the powers of the Presidency. So, for example, we do not use the autopen for executive orders, presidential memoranda, decision memoranda, nominations, appointment orders or commissions, or bills to be signed,” he wrote.

“We do not use the autopen even for more routine purposes, such as the invitation of foreign leaders to the White House. The President personally signs all of these, in the presence of witnesses. We will occasionally use the autopen when a single document requires multiple presidential signatures, or when multiple copies of a single document require signing, but only after the President has personally signed off and only at his direction.”

A memo dated Jan. 28 and also reviewed by The Post grants Scharf and White House Chief of Staff Susie Wiles the authority to use the autopen “for all matters.” Scharf’s deputy and the president’s executive clerk are allowed to make the call at Scharf’s direction.

The White House director of correspondence, who manages lower-stakes public communications such as congratulatory messages to Americans on significant life milestones such as birthdays, is also allowed to use the autopen “for standardized policy materials after clearance by [Schart]” and for “Presidential messages in accordance with specific direction,” according to the January memo.

Autopens have been used by presidents since Lyndon Johnson in the 1960s — most notably for letters to children and similar trivial matters — but the use has expanded over the years, with then-President Barack Obama in 2013 using an auto-pen to sign a major spending bill.