Final answer:
A primary source document from the National Archives website is a letter from President Abraham Lincoln to General Ulysses S. Grant during the Civil War, discussing Grant's military successes and strategic plans.
Step-by-step explanation:
A primary source document that can be found on the National Archives website is a letter from President Abraham Lincoln to General Ulysses S. Grant during the Civil War. The letter, dated August 9, 1863, addresses Grant's recent military successes and his strategic plans for the war. The document is a primary source because it is an original and direct record of a historical event, written by a person who was directly involved in the event.
Link: Letter from President Abraham Lincoln to General Ulysses S. Grant