Hola and welcome to the forum.
Do a search, at top of screen, for 'portugal winter'.
Several threads will appear with information you may find useful.
Else try 'winter' and get a general idea about things that needs to be thought of for doing a winter camino.
Walking in winter is fantastic, but some of the challenges are heavier backpack, fewer albergues are open, weather and temperature.
With some good planning, especially equipment wise, the real challenge is the weather.
Low sub-zero degrees and potential snow storm has to be taken very serious, but again, with a wise approach it should be no problem for most.
Some of the positive about winter walks are solitude, fewer (but maybe stronger) pilgrim relationships, very friendly locals.
Good luck planning your camino and do ask further, as this forum is filled with experienced and sharing members.
Buen Camino
Lettinggo