Run Windows Recovery before selling PC

The laptop had windows 7 when I purchased it. I upgraded for free to Windows 10.

Question: If I run "Recovery" -> "Remove everything" will I end up with Windows 7 or Windows 10?

HPF said:

...If I run "Recovery" -> "Remove everything"...

Welcome to TenForums @HPF

I presume you mean the 'Reset this PC' option in Settings > Update & recovery > Recovery.

This will reinstall Windows 10 using the system files already on your PC as the source. The option to 'remove everything' removes all personal files and installed apps. This includes any OEM utilities. Only OEM utilities that came with a pre-installed Win10 would be reinstalled, so you'll loose any that came with its original Win7. You may be able to download them from the manufacture's site if you want to reinstall any of them.

More details in this tutorial:

Reset Windows 10

cereberus said:

As part of "reset my pc", there are are two options - one to remove everything as you say, and one to remove everything and securely wipe drive for selling pc i.e. all data is nuked so it cannot be recovered by recuva etc. The latter option takes longer but is more secure.

Are you sure the secure erase of the hard drive is part of reset this PC options? Reset this PC from inside Windows uses files from the Windows folder itself to reset Windows, so if the drive was securely erased, how could it reset Windows from files that were on the drive that was supposedly securely erased? I've always known securely erasing a drive to be a two step process - you boot into the program that does the secure erase of the drive, and then you do a clean install of Windows from an external media source that contains the installation files.