Heretofore is a very formal adverb that simply means before the current time, or until now.
Hitherto is another very formal adverb that means until the current time or before now.
The two words are synonyms and severely unpopular. Even in legal and scholarly realms it is better to use simpler synonyms such as before, previously, and so far.
Interestingly, there are a few related terms that have also gone out of favor.
Hitherward is an archaic word that describes a direction as toward somewhere or someone.
Theretofore is an adverb that means to a certain point of time in the past.
Hereto is an adverb that describes an action as happening to a particular piece of writing or document. It is almost always used with the verb attached.
Johnson, a heretofore healthy, vibrant Pasadena photographer with a head of auburn hair, had been diagnosed in July 2010 with a cancerous tumor known as a sarcoma in her hip socket. [Forth Worth Star Telegram]
The spirit of Richard Burton looms large over any rendering of Under Milk Wood: the actor’s sonorous vowels, on display in what has hitherto been considered the definitive cinematic version from 1972, somehow seem to perfectly embody Dylan Thomas’ effusive, garrulous poetry. [The Guardian]
Yet, Iran’s support for Syrian dictator Bashar Assad during the civil war damaged theretofore close relations between Iran and the political wing of Hamas, who supported the Sunni Islamist factions opposing Assad. [The Washington Times]
In a document prepared by university controller June Gutknecht, the school writes that “the proposed amendments to Regulation FGCU-PR7.001 Tuition and Fees, attached hereto as supporting documentation, do not impose an increase for tuition and fees.” [Naples Herald]