Should you capitalize "Will" (as in a "Last Will and Testament")?

In general it should not be capitalized, but there is a fashion lately to capitalize it. The fashion seems to be arising among lawyers, whose capitalization sense seems to have become miscalibrated by the practice of capitalizing specifically defined terms in legal documents.

This may also be the reason behind the change in style in the broader business community, where it is lately popular to capitalize common nouns such as company, product, sale, or what have you. You even occasionally see capitalized verbs.

There is probably also some feeling that capitalizing will somehow makes it clearer that it is the legal document sense of the word rather than the desire or intention sense. But really, there's rarely any such ambiguity, and, frankly, using a capital letter doesn't actually reduce ambiguity.

Outside of an actual will, or another legal document that concerns a specific will, there is no more reason to capitalize will than there is to capitalize contract, affidavit, deposition, instrument, summons, or any other word denoting any other sort of legal document.