What is identity H?

[tonylondon]

This isn't specifically an XX problem as the same thing happens in other programs, but I'd be very interested if the experts on this forum have the answer.
If I create a document in XX using, say, Arial or Times New Roman and then export it as a PDF everything seems fine.

When I open the file in Acrobat and use the touch-up text tool I'm told the font isn't available and has to be substituted, and sure enough, after using the tool an extra font pops up in the used fonts dialog.

Attached are the dialog boxes,

Any explanation gratefully received,

Tony