For up to about 2500 tickets, you can run this query from the Stat Builder:
If you have more than 2500 tickets, you can run the same query as above, but with multiple WHERE constraints. The current limit is set to prevent any single query from overloading the system. You would use clauses like this:
WHERE tickets.id >= '1' AND tickets.id <= '2500'
WHERE tickets.id >= '2501' AND tickets.id <= '5001'
It should only a few seconds to run each report, and a few seconds update the query. Each output can be exported to CSV/PDF. Even for large amounts of tickets, it should only take a few minutes to iterate through them all with this method.
If you have added a lot of custom ticket fields, this may not work (Reports can only include up to about 55 fields). In that case, run a query which specifies the ticket fields individually. Replace SELECT tickets.* in the query above with:
SELECT tickets.id, tickets.subject
The full list of ticket fields is available on the Reports Manual.
You will then be able to export the result in PDF or CSV format.
If you have more tickets than the Report Builder can output, you will need to export your tickets using the DeskPRO API (requires programming skills).