Can I transplant an indoor orchid outside?

That will depend on your location?

Only in the far south from what I understand, like Florida, then if it get close to freezing occasionally they might still die, or make it, depending on the temp. and being covered . .

I've never had any luck with indoor plants outside. If you just need it out of the house, you could try it, but I wouldn't expect it to live.

You don't "plant" an orchid, they are air plants. A home store sells bark to use to sit your orchid into, but putting dirt on them will kill the plant. Just put them in the crotch of a tree or branch, fertilize with 1/2 strength fertilizer about once a month. Unless you live in a very dry place, the rains are enough. They burn in the sun so make sure it's shady, again in a tree is excellent. I live in Florida and have a whole bunch in trees or hanging on trees. Good luck.

This is an excerpt taken from the American Orchid Society:

Properly selected and cared for, orchids can be among the showiest and most exotic of all garden or patio plants. There are many areas throughout the southern and central United States where temperatures for a good portion of the year are compatible with the needs of many orchids. Some coastal areas are nearly frost-free year round. In these areas, with some protection from excessive sun, wind and rain, lovely orchid plants can be successfully cultivated on the patio or as a part of the landscape. In frost-free areas, the plants can be left in place all year. Where frost or temperatures below 40° F threaten, plants can be brought into the home to be grown on windowsills, under lights or on an unheated patio where the coldest temperatures are avoided. The trick is in selecting plants that are already adapted to your particular area.