I get a new passport, but I have a valid Vietnam tourist visa in my old passport. Can I travel with both passports to Vietnam without applying for a new visa? (I'm a portuguese citizen).
You can still have your current visa transferred to your new passport. At Saigon airport, you’ll have to pay 15 USD for this work.
Another persons experience below:
Arrived at Saigon airport with valid visa in a cancelled passport, together with my new passport. At Saigon airport I had to pay USD 15 to have the visa transferred from the cancelled passport to my new passport.