What sort of files are these?

[Stevekir]

They are included in FreeFileSync's list of files to be updated. I have never seen them listed before for a backup. X: is my internal HD which contains only documents, Pictures etc. No programs or system files.

What do they do and why would they be included in a backup of a drive that has only docs, pictures etc?

The first image is representative of several similar files with different numbers.

Thanks.

 

[D3LL]

WER, is Windows Error Reporting, these are probably just log files.
https://msdn.microsoft.com/en-us/library/windows/desktop/bb513613(v=vs.85).aspx

 

[Taplice]

The $WINDOWS.~BT folder came from Windows, or more precisely a Windows update. The $WINDOWS.~BT folder is hidden. It exists at the root of the drive you’ve installed Windows to, includes files to upgrade Windows, and also, once you do upgrade, the old OS goes into that folder.
It should be perfectly safe to delete it, as long as you don't want to upgrade or downgrade Windows.