Learn Polish: Ten zapis jest długi i niestety go nie doczytałem. - This provision is long and unfortunately I didn't read it to the end.

The prefix do- in doczytałem specifically emphasizes bringing an action to its final conclusion. While nie przeczytałem just means "I didn't read it" (you might not have even started), nie doczytałem specifically highlights that you started reading it but didn't make it to the very end.

Since doczytać is perfective, what is its imperfective equivalent if I want to say "I am finishing reading it right now"?

The imperfective counterpart is formed by changing the ending to -ywać, making it doczytywać. You would say Właśnie to doczytuję to mean "I am finishing reading it right now" or "I am reading it to the end."

Why is the pronoun go placed before the verb phrase (go nie doczytałem) instead of at the end of the sentence?

Short pronoun forms (clitics) like go prefer to anchor themselves to the middle of a clause and generally avoid the very end of a sentence if possible. Placing go right after the adverb niestety sounds much more natural and rhythmic to Polish ears than saying niestety nie doczytałem go.

I usually think of zapis as "saving" (a file) or a "record". How does it mean "provision" here?

The noun zapis comes from zapisać (to write down) and broadly refers to anything officially written down. In legal, business, or formal contexts (such as reading terms and conditions or a contract), it is the standard word for a "provision", "clause", or "stipulation".