The question being: since “well” is an adverb, not an adjective, we do not hyphenate “well documented”. The doctor performed a well documented procedure. The adverb “well” cannot modify the noun “procedure” so there can be no confusion.
Similar: an awfully big adventure and not an awfully-big adventure.
When “well” is replace by something not clearly an adverb, then probably you should hypenate: the three-hour tests
A comment by @Chemomechanics suggests I am wrong. And I have come to the conclusion that I am, indeed, wrong.
Fowlers' Modern English Usage (3rd edition) even has an entry on well and well-. They note “widespread uncertainty” on well followed by a participle. But they advocate a hyphen for attributive uses (a well-documented procedure) but not for predicative uses (The procedure is well documented).
As a mathematician I often see “well ordered set” and similar phrases in mathematical literature. My original tendency was to write it with hyphen (well-ordered set) and found that was not the standard, so I tried to wean myself from that practice and write without (well ordered set).
But today, prompted by Chemomechanics’ comment, I did some searches of mathematical literature. To my surprise, nowadays “well-ordered set” far outnumbers “well ordered set”. I guess I can therefore lapse back to my original tendency.
Of course, by the rule quoted in Chemomechanics’ comment, I should still write the -ly cases without hyphen: "partially ordered set", "totally ordered set", "linearly ordered set".