Any extended time indoors will shorten its lifespan significantly. Conifers are not houseplants :-) When I worked at the nursery, we always instructed those purchasing a live tree with hopes for replanting to move the tree indoors for a week or less. (emphasis on the less). Make sure the rootball is fully hydrated and site in the coolest location away from any heat sources or drafts.

Mrs. Claus keeps red spruces (Picea rubens) as houseplants, to help them survive the nibbling reindeers of her husband :-)

if you had transplanted it last fall or winter.. and grew it in the pot all summer long.. getting over all those stresses ...

then JUST MAYBE.. you could get away with having it in the house THIS xmas ...

when i tried this with fall purchased potted trees... i closed off the living room from all furnace heat.. and cracked open a window for proper humidity for a tree .. that room was very cold for the 2 weeks... in fact.. just like it was outside ....which is where the trees should be ...

i also had the holes dug outside.. with bags of fall leaves in the holes.. and all the soil in the heated garage.. so that when i took them out.. i could throw them in the hole.. water it as the ground hadnt frozen under the leaves.. back filled them properly.. and then used the leaves to put a giant pile of leaves around each tree ..

as you can see.... you have a lot of variables to consider and overcome.. to be successful here..

all that said.. they are free.. why not give it a try ... worse that could happen would be you kill it.. which is exactly what would happen if you bought a cut tree anyway ...

soooo.. go for it..

ken

ps: try to place them away form the forced air furnace if you have one.. hot blowing air on a transplant would not be approved ...