"To forge a letter" means to create or make a fake letter, usually with the intention of deceiving someone by making it seem like it was written by someone else. Full definition
Successfully argued Standard Bank v Bank of Tokyo [1995] 2 Lloyd's Rep. 169, a claim arising out of forged letters of credit circulating on the London forfaiting market. (essexcourt.com)
Directed by Marielle Heller (The Diary of a Teenage Girl) from a script based on Israel's memoir, the October 19 release picks up in 1991, when Israel is struggling to pay rent and resorts to forging letters from famous authors. (metacritic.com)
A US congressional inquiry has found more than a dozen forged letters to members of Congress purportedly from voters opposed to a climate change bill — including a number from old people's homes. (heatisonline.org)