on paper vs theoretically

on paper and theoretically both are adverbs.

Word	Noun	Adjective	Verb	Adverb
on paper	No	No	No	Yes
theoretically	No	No	No	Yes

As adverbs, on paper and theoretically are synonyms defined as:

on paper (adverb)	theoretically (adverb)
as written or printed	in theory; according to the assumed facts
in theory; according to the assumed facts	in a theoretical manner