Questions & Answers about Я нашёл нужный документ в папке на столе.
Нашёл is the active verb найти = to find (you found something).
Нашёлся is the reflexive form найтись = to be found / to turn up (the thing “got found” on its own):
- Документ нашёлся. = The document turned up / was found.
In past tense, Russian verbs agree with the subject in gender (singular) and number:
- я нашёл = I (male) found
- я нашла = I (female) found
- мы нашли = we found (no gender distinction in plural)