We need to evidence the agreement with these forms.
Is this usage predominantly American?
While the vast majority of online dictionaries (as found at onelook.com) list evidence as a transitive verb, in virtually all examples, the verb is used passively, as in
Her curiosity is evidenced by the number of books she owns. [American Heritage Dictionary]
The active usage, such as the Questioner offers, does not seem common.
An ngram search of he evidences and he evidenced, as examples of active use, does show some significant usage, but mostly using the term to mean to make evident; show clearly, rather than to give proof of or evidence for [both from Collins]
While many such usages are clinical, both in medicine and psychology, even well known literary works partake
He drove them all, maids, matrons and widows, and toward all he evidenced the same uncompromising contempt. It was obvious that he did not like women, Melanie excepted, any better than he liked negroes and Yankees.
[Margaret Mitchell, Gone with the Wind)
Is “evidence” as a verb an Americanism?
The answer to the Original Poster's question is, no! The first datable attested example from the Oxford English Dictionary is from Atheomastix by Martin Fotherby, Bishop of Salisbury, from 1622:
The testimonie of neither of them..doth so euidence the matter, as the things themselues doe.
The OED lists seven attested examples of to evidence with this meaning spanning the seventeenth to nineteenth centuries, six of which were from Britain and only one of which from the United States. This seems pretty decisively to show that evidence, the verb, shouldn't be considered an Americanism.
NB: this particular page entry in the OED has not been fully updated, and was first published in 1894!
Here's the relevant definition from the Oxford English Dictionary [login needed]:
- trans. Of things: To serve as evidence for; to attest, prove. Rarely intr. to evidence to
[The citation for the quote and references from the OED are is follows: "evidence, v." OED Online. Oxford University Press, September 2014. Web. 16 October 2014.]
Evidence can be used as a verb according to Merriam Webster
Its usage as a verb is not common on either side of the Atlantic.
In your case, I would use:
"We need to formally document the agreement with these forms"
I am British, and one who does not hesitate to say if I think our American cousins are taking liberties with the language. But I make liberal use of evidence as a verb, both in the active and passive voices.
David Cameron's sensitivity to the issue of his late disabled son, was evidenced by the way he responded to Ed Miliband's question in the House of Commons
He evidenced his disapproval with a loud tut-tut.
I see nothing whatever wrong with these sentences. So from what others have said I am tending to the view that it is more idiomatically British than American.
I was corrected by a colleague when I used the expression "as evidenced by". I was told directly that evidence is a noun and the correct verb to use is "to evince".
Whilst "evince" is a little known word, the definition "indicate or exhibit (quality)" suggests that it is the correct verb to use and that "to evidence" came about through common usage.