I want to take a high speed train from Lisbon to Porto the day after entering the country. Can I purchase tickets from home, before I leave for Portugal?
Yes, official Portuguese rail is www.cp.pt.
Thanks so much for that fast and informative reply!
Hope you enjoyed your train ride. I found the Alfa Pendular comically slow and rickety compared to other high speed trains I’ve taken, including ICE and Shinkansen
Seat61 has some additional information you might find helpful. Tickets are cheaper if you buy them in advance. I actually flew into Lisbon and then took the train the same day to Porto, taking a nap while traveling. I thought the train ride was pleasant, but then I don't have a great deal of European train travel experience for comparison.
https://www.seat61.com/trains-and-routes/lisbon-to-porto-by-train.htm