Hi K. I'm Greg, 10 years awarded Windows MVP, here to help you.
There is no possible way Bitlocker can install itself. It doesn't even apply to Home version without a major hack being done, which also cannot possibly be done by itself.
If ti was Pro version it could have been done at the factory but they should have seen to it the key was stored in the new owner's Microsoft Account. Check there now just in case:
https://support.microsoft.com/en-us/windows/fin...
If not try these to see if you can turn it off or uninstall it:
https://helpdeskgeek.com/windows-10/how-to-turn...
https://www.repairwin.com/how-to-remove-bitlock...
Then see if you can recover your files:
https://www.howtogeek.com/263561/how-to-recover...
If not then there's one last thing to try before wiping the drive with Diskpart Clean Command to get rid of Bitlocker and reinstall WIndows. Try rescuiing your files using bootable media by one of these methods:
https://answers.microsoft.com/en-us/windows/for...
To create bootable media Follow the steps toward the bottom of the download page here in the section "Using the tool to create installation media:"
https://www.microsoft.com/en-US/software-downlo...
Then wipe the drive with Clean Command:
https://www.tenforums.com/tutorials/85819-erase...
and Reinstall Windows doing this gold standard Clean Install that compiles the best possible Install of Windows which will stay that way as long as you stick with the tools and methods given, has zero reported problems, and is better than any amount of money could buy: http://answers.microsoft.com/en-us/windows/wiki....
Feel free to ask back any questions. Based on the results you post back I may have other suggestions if necessary.
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Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.
Feel free to ask back any questions. Based on the results you post back I may have other suggestions if necessary.
______________________________________________
Standard Disclaimer: There are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.