as, like, _

[Tukanja]

Please someone tell me the correct form of the sentence below

The monograph can be considered a historical document of a time that has had a major impact on business and development of this company.

The monograph can be considered as a historical document of a time that has had a major impact on business and development of this company.

The monograph can be considered like a historical document of a time that has had a major impact on business and development of this company.

Also should the a or an have been used before the word historical?

[Joe]

I think the sentence you want is #2.

#3 is not English.

historical | a/an
Because the stress is on the second syllable (another example is "habitual"), in speech there is a chance that the "h" will not be heard (starting the unstressed syllable). This is the reason why "an" is sometimes used before such words as "historic(al)" and "habitual". Both "a" and "an" are equally correct, but using "an" may seem too formal or even pretentious in normal usage.

[Tukanja]

Yes, the second one's mine.