Understanding a company's place in the competitive landscape is a key piece of company research. Any of the databases listed in the Company Profiles tab will provide lists of competitors. Think about the criteria that was used to create the list to determine whether it is comprehensive and relevant to your analysis.
The 10-K will include a statement (Part 1, item 1A: Risk Factors) which nearly always discusses competition in the industry. Individual competitors may not be named outright, but the filing company will explain which types of companies they see as competitors and which activities or qualities are perceived as competitive threats. Only publicly-traded companies file this document. Find the 10-K in the Investor Relations section of the company's website, or by searching the SEC's EDGAR database.
See the Market Share & Rankings resources below for additional ways to find competitors.