To count the number of words in a document, you would use the:

Word processing software like Microsoft Word offers various tools to analyze and manage documents. The question asks which tool is used to count the number of words in a document.

• Word Count is the correct answer. This feature is specifically designed to provide statistics about a document, including the total number of words, characters (with and without spaces), paragraphs, and lines. It's invaluable for writers needing to meet specific length requirements.
• Thesaurus is incorrect; its purpose is to help users find synonyms and antonyms for selected words, enhancing vocabulary and writing style.
• Spell Check is incorrect; this tool identifies and suggests corrections for spelling and grammatical errors within the document.
• Translate is incorrect; this feature converts text from one language to another, facilitating communication across different languages.

Thus, for a precise word count, the dedicated Word Count tool is essential.