Finding your files
Every purchase lands in Library immediately after checkout. You also get an email receipt linking to the order. Downloads only work while you are signed in to the account that bought the product.
Re-downloading
Files stay available in your Library for as long as your account exists — there is no expiry date. There is a limit of 30 downloads a day across your purchases, which is plenty for normal use and stops a leaked session from emptying a library.
Versions
When a seller uploads a new version you get it free. The product page lists the version history, and earlier versions you bought stay downloadable, so an update never breaks a project mid-flight.
File formats
Each listing states its formats and software requirements in the Details section. Check that against your tools before buying; a product file is a single download of up to 50 MB.