The following was taken from the book “Português Do Dia-a-Dia” by Prof. Sérgio Nogueira Duarte da Silva. If you get a chance to purchase the book, I do recommend it. As for the participle and the lesson below, one will often see the past participle of pagar, aceitar and prender (pago, aceito, preso) while the rest of the examples are seen to a lesser extent. Keep in mind that you will hear the ‘wrong’ way used in informal Portuguese (ie. tinha entregue), but wrong and right, as you may find, are debatable. The participle lesson starts with the example below.
Ex. Ele tinha ENTREGUE or ENTREGADO os documentos?
The correct form is “tinha entregado“. When the verb has two participles (abundant verbs), the rule is the following: With the auxiliary verb ter (or haver), the regular form (with the ending of -ado or -ido) should be used.
Ex. Ele tinha entregado os documentos.
With the auxiliary verb ser (or estar), the irregular form should be used.
Ex. Os documentos foram entregues por ele.
Observe other examples:
Ter (or Haver)/ Ser (or Estar)
aceitado/aceito
acendido/aceso
elegido/eleito
entregado/entregue
expulsado/expulso
extinguido/extinto
imergido/imerso
isentado/isento
matado/morto
morrido/morto
prendido/preso
salvado/salvo
submergido/submerso
suspendido/suspenso
Observations
On principle, this rule applies itself to the verbs ganhar (ganho and ganhado); gastar (gasto and gastado); pagar (pago and pagado); pegar (pego and pegado);
Ex. Isso foi ganho, gasto, pago e pego.
The regular forms are rarely used in Brazil. Many scholars already accept the irregular forms, even with the verbs ter and haver.
Ex. Ele tinha ganho, tinha gasto, tinha pago and tinha pego.
The verbs trazer and chegar aren’t abundant. They use just one participle: trazido and chegado. The forms trago and chego are inacceptable:
Ex. Isso foi trago por mim; Ele tinha chego atrasado.
The correct form is: Isso foi trazido por mim; Ele tinha chegado atrasado.