No you probably won't. Do you really think the other company will stand for you copying their name without a fight? Just adding a few letters to their company name will likely cause confusion as to source of products or services and thus will most likely be trademark infringement. You need to see a trademark attorney for a free consult. You are unquestionably in over your head.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Maybe, it depends on what IP rights the other registrant has. If the registrant of the other domain name has a registered trademark, then that could be a basis to prevent you from obtaining a minor variation of that domain name or use a different extension. The more important question is whether someone else has a trademark that could prevent you from using that name in the marketplace. If the trademark is used for a different good or service, you might be clear. You need to consult with a trademark attorney. Good luck.
This answer is for informational purposes only. It is not intended as specific legal advice regarding your question. The answer could be different if all of the facts were known. This answer does not establish an attorney-client relationship.
Please see my reply to your other query. You need an IP lawyer before you do anything else.
Avvo doesn't pay us for these responses, and I'm not your lawyer just because I answer this question or respond to any follow-up comments. If you want to hire me, please contact me. Otherwise, please don't expect a further response. We need an actual written agreement to form an attorney-client relationship. I'm only licensed in CA and you shouldn't rely on this answer, since each state has different laws, each situation is fact specific, and it's impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.
Your problem arises under trademark law. Trademark rights arise from use in commerce. If someone purchases a domain name and uses the main words contained therein as a trademark, it acquires common law trademark rights even without registration. Before you can proceed, you need to retain counsel to conduct a "trademark clearance". You simply cannot do this on your own--because I can tell from your questions and comments that you do not have even a basic understanding of intellectual property law issues. You need a lawyer---and the general discussions on this web-site are not a proper substitute for retaining counsel.