Excel - want filename in header

[Martyuk39]

I want to put the filename in the header, eg. order number &[File], but it displays the .xls - is there any way I can better this?

Basically I want a batch of spreadsheets referring each to a sequential list of orders

[edit] it just occurred to me that it's system-dependent - if registered extensions are hidden then they won't show up on the header, but I'd like a slightly more reliable way if there is one!

Thanks
Martin