We usually say we work "at" or "for" a company--both are common. Use "since" and "until" alone, or use the pair "from...to" Mr Black has been working at/for this company since April 25, 2018. Mr Black has been working at/for this company until now, but he is considering leaving it. Mr Black worked at this company from 2015 to 2016. Mr Black has been working at/for this company from April 25, 2018 to the present. Like Rena, I prefer the first choice: Mr Black has been working at/for this company since April 25, 2018. the present perfect continuous tense makes the "until" portion redundant.

Mr Black has been working at this company since April 25, 2018 Since this is in the present perfect continuous, ('has been working") you don't need "until now/ etc" because it automatically means that he still works there.

Mr Black has been working at this company since April 25, 2018 until present. I'd say that (until present/to the present day/up to the present day/till present) are all correct and can be used interchangeably, but they give the idea that he's not going to be working there anymore. However, if you meant that he's been working and will continue to work at that company, then it's better if you don't use the final part. Mr Black has been working at this company since April 25, 2018.