He took you under his wing and he embraced your presence in his family. He put in the effort to make you feel comfortable being part of his family. Appreciate his efforts and celebrate him greatly on his birthday. Send this ecard too.
Today is the day to say 'thank you' to your father-in-law for being such a great role model to you. The fact that he has embraced you into his family is an action that you need to appreciate more. So send this ecard on his birthday.