1. I had paid my bills until now.
2. I have paid my bills until now.
3. I have paid my bills so far.
Hi, Subhajit: The link you've posted is faulty. However, even if the link led to an actual post, the thread itself is technologically defective at the present time. A reply to the original question does exist, but it is in cyber-limbo. This is one of the threads that got broken in the change in platforms. Soon we hope to have all the broken threads put back together again.
The best sentence of the three is (3), and the worst is (1). There would need to be a really good justification for using "now" with the past perfect. It's conceivable in the context of literary fiction, but in general it's wrong. You need the present perfect in (3), with "so far," though the past perfect is conceivable, again, in the context of literary fiction.
As for (2), it is imperfect. The non-official non-native member who replied originally did not take issue with it, and that is why I am not quoting the answer. Sentence (2) needs one of two adjustments. You can either change "until now" to "up to/till now" ("I have paid my bills up to now"), or you can separate "until now" from the clause with a comma or dash ("I have paid my bills -- until now").
Notice that, in both revisions, the present perfect is used. It may interest you to know that there are formal adverbs that work here: "hitherto" and "heretofore" (both mean the same thing): "I have heretofore paid all my bills." In very formal discourse, we also have "theretofore," and that works with the past perfect: "I had theretofore paid all my bills." (theretofore = up to/till then)