Pearl Tytell, the matriarch of a family of questioned-document examiners whose intricate knowledge of paper, ink, handwriting and typewriters made her a prominent investigator of frauds, forgeries, tax evasion and poison-pen letters, died on Sept. 26 at her home in the Riverdale neighborhood of the Bronx. She was 104.

Her death was confirmed by her daughter and only immediate survivor, Pamela Tytell.

Mrs. Tytell worked with her husband, Martin, at their typewriter repair and rental business on Fulton Street in Lower Manhattan, which branched out into the scientific examination of documents in the early 1950s. A rare woman in a male-dominated field, Mrs. Tytell ran that end of the business and trained her son, Peter, a widely known examiner of documents until his death last year.

Mrs. Tytell was an expert witness for the federal government in 1982 in the tax-evasion case against the Rev. Sun Myung Moon, the head of the Unification Church. By analyzing changes in his handwriting — particularly how his printed “S” had turned cursive — she testified that he signed checks in 1974, not in 1973 as his lawyers had said.

At another point, Mrs. Tytell used paper-mill records and her knowledge of watermarks to prove that a piece of paper had not been produced until after the date written on it.

“She was an exceptional witness,” Martin Flumenbaum, a prosecutor in the case, said in a phone interview. “She dominated the courtroom. I remember the jury being enthralled by her testimony.”

Mr. Moon was convicted of conspiracy to defraud the federal government and of filing false income-tax returns. He served nearly a year in prison.

Mrs. Tytell “worked on every case that my father did,” Pamela Tytell said. “Clients often hired my father, but she did all the work. She took some of their high-profile cases because my father wasn’t good on the stand.”

But mostly she operated out of the public eye, examining wills, contracts, receipts, checks and many other types of documents for a half-century.

Before Roe v. Wade established that abortion was a constitutional right, she and her husband investigated a series of anonymous letters sent to a doctor’s patients and the parochial school where he volunteered, saying that he was operating an abortion mill.

Mrs. Tytell told The Daily News in 1972 that she had spotted one phrase repeated in the letters — a reference to the doctor’s wife as“a dirty housewife.” She surmised that the writer was a female relative, and it turned out to be the doctor’s sister. Posing as a typewriter repairman, Mr. Tytell went to the woman’s office, got a sample of her writing from her typewriter and proved the connection.

“We get one case a week of poison-pen letters,” Mrs. Tytell said. “They can destroy a career, a reputation, a marriage or a whole life.”

In one of her best-known cases, she was hired in 1972 by International Telephone and Telegraph to analyze a politically explosive memorandum written a year earlier by one of the company’s lobbyists, Dita Beard (who denied writing the memorandum). Its existence was revealed by the investigative journalist Jack Anderson.

It suggested a connection between the settlement of a government antitrust lawsuit against I.T.T. and a pledge by the company to pay $400,000 in costs for the 1972 Republican National Convention.

A report issued by I.T.T. said that Mrs. Tytell and a chemist, Walter McCrone, had used “microscopic, ultraviolet fluorescence and highly sophisticated micro chemical analyses” of the memorandum and other samples that had been typed on Mrs. Beard’s typewriter between June 25, 1971 (the date on the document) and February 1972. They determined that the memo had most likely been written in January 1972, nearly six months after the antitrust settlement, meaning a connection to the payment was not likely.

Their report — submitted to the Senate Judiciary Committee, which investigated the financial pledge made in the memo — contradicted the F.B.I.’s analysis of the document, which suggested it had been written on June 25.

Pearl Lily Kessler was born on Aug. 29, 1917, in Manhattan and grew up in Brooklyn. Her parents were Jewish immigrants from Europe: her father, Harry, was a tailor from Austria, and her mother, Yetta (Feigenbaum) Kessler, left Poland when she was 2.

In 1938, Pearl was working in the accounting department of a company in the Flatiron Building in Manhattan when she met her future husband. He came to her office seeking a rental and repair contract and, while there, asked her to dinner. While they did not go out that night, he returned the next day and told her, “Come work for me and I’ll marry you.”

She soon went to work for him, and they married in 1943, while Mr. Tytell was in the Army.

In 1950 came a major change for the Tytells’ business.

Lawyers for Alger Hiss, the former State Department official who had been convicted of lying to a grand jury about passing secret information to a Communist agent, Whittaker Chambers, hired Mr. Tytell to prove that a typewriter’s print pattern can be reproduced. At his sentencing, Mr. Hiss accused Mr. Chambers of committing “forgery by typewriter” — making it appear that the documents had been produced by Mr. Hiss’s typewriter.

Mr. Tytell spent two years building a typewriter that had a print pattern indistinguishable from Mr. Hiss’s Woodstock model, to prove that the disputed documents could have been fabricated. Mrs. Tytell did the research on the parts and characteristics of the typefaces that had to be duplicated. Their work became the foundation of Mr. Hiss’s appeal, although it was ultimately unsuccessful.

After the Hiss case, Mrs. Tytell took courses in paper, photography ink, type styles and handwriting; in 1951, the couple opened the Tytell Questioned Document Laboratory, which became the focus of her work and eventually, her son’s. In the 1960s, she graduated from New York University with bachelor’s and master’s degrees.

“Handwriting talks to me,” she told The Daily News. “So do typewriters, ink and paper.”

Her clients included insurance, oil, media and railroad companies, as well as banks, courts, law firms and government agencies. For many years she also worked with the Board of Elections in the Bronx and Manhattan, helping to confirm voters’ identities by comparing their signatures on absentee ballot envelopes with those on file.

In 1963, Mrs. Tytell debunked the claim by a Chicago woman named Eugenia Smith that she was the Grand Duchess Anastasia of Russia, the daughter of Czar Nicholas II, and had somehow survived her family’s execution by Red Army guards in 1918. (DNA tests later ruled out at least one other woman, Anna Anderson, who made the same claim.)

Working for Life magazine, Mrs. Tytell compared specimens of Mrs. Smith’s handwriting in Russian with script known to have been written by Anastasia. She found noticeable differences in the way Mrs. Smith wrote the letter “e” and errors in her use of the Russian alphabet, including writing “inoculate” when she was asked to write “greetings.”

More broadly, Mrs. Tytell wrote in her report to Life: “In gross appearance alone, the two sets of documents are markedly different. When examined letter by letter, the differences are even sharper.”

For several years after her retirement in 2001, Mrs. Tytell consulted with her son.

“Every other Sunday he’d show her the cases, and she’d give her opinion,” Pamela Tytell said. “He’d say, ‘Boy, some of the things she said, I didn’t think of.’”