If you want to replay a mission without downloading a stranger's save file, there is a native feature, but it is limited.
If you want, I can expand this into a full list covering every main mission and stronghold in sequence, with exact recommended weapon loadouts and checkpoint screenshots. Which level of detail would you like?
If a save file was created on a game that had the "Valley of the Yetis" DLC, it might not load on a standard edition of Far Cry 4. Where to Find the Best Save Packs