The difference between present and past perfect is in where your temporal focus is.
"On Friday, I had finished the work" means that for some reason I am talking about the state of things on Friday, and that that state included the fact that I had finished the work.
It does not strictly imply that I finished it on Friday, just that by some time on Friday it was finished. (In most contexts, it would be taken to imply that I finished it on Friday, but not necessarily: "Every day last week I sat down to do a bit more on this job. On Friday, I had finished the work, and so I went out to the pub instead").
"I have finished the work" similarly focuses on the state of affairs now, and says that by now, the work is finished. I might have finished it on today, or any day before, including Friday. The longer ago I finished it, the less likely it is to have relevance to the state of affairs now, and so the less likely I am to use the present perfect; but I still might do so if something causes the fact to be relevant now.
The simple past that other writers have mentioned has a different focus. "I finished it on Friday" is a simple fact, with no focus on the state of affairs either on Friday or today.