only if its the right model for the door opener. Even if it is you can easily change the code so its safe to use.
find the make and model number and go toe the manufacturer's website and look for manual. It should describe the process there.
Search the instructions to the product on line and see what it says.
Can you call the people who made the thing?
Dependant on the make and model of the opener and remote, you can purchse a chipset for the opener and remote. See a reputable garage door dealer for the details.
Yes, it changes the code so the previous owner wont be able to open the garage again.