import deck
Deck module allow you to import any stock file format import . See import cards for more details
MTGCompanion have many sniffer to get deck directly from online website.
You can manage plugins here
Select Import / Online / Website Menu
The Panel allow you to select the website 
if the selected sniffer allow you to filter search with a card in deck, you will be able to choose a card, and will be add to the search filter
click on 
to choose the card, or
to remove it.
Then apply suggested filters and choose your deck and press 
button
