I was adopted - would it be possible to trace my heritage from a DNA test? I know nothing about my original family.?

Yes. DNA tests are based off of DNA not what you know about your family

I think they can trace where your ancestors came from.

Genealogy DNA tests will not tell you who your specific ancestors were. Now if the company you choose happens to have cousins of yours going back several generations in their database and they notify you of those cousins and you are able to make contact with them, you might learn some things.

No heritage is that which is inherited. As you were adopted you will "inherit" nothing from your biological parents. What DNA can reveal is the ancestry of pat of your biological lineage, as you only receive a half your DNA randomly from each parent. which is why siblings can have different DNA results. You could learn about your ancestry in general, but not about specific ancestors.

No it would not help.

NO it is most doubtful that your actual family could be traced/. DNA indicates general findings not specific families.

Ask your adoptive parents what they know about your biological parents. If your adoption records are sealed, ask to have them opened and start the legal process for doing so.

it would be possible. there are more than 7 billion people in the world. and if you will take dna test to them one by one, you will finish at year 3100

It would give you percentages of different countries.