Facebook filed to raise up to $5 billion in a highly anticipated public offering today. The company revealed that its annual revenues were $3.71 billion in 2011, with net income of $1.002 billion.

Advertising accounted for 85 percent of revenue. The remainder comes from fees and payments or transactions through Facebook Credits, the company’s now mandatory virtual currency. Facebook doesn’t say much about how it plans to spend the funds other than saying it may go toward acquisitions of other businesses or assets. To that end, Facebook actually already has more than $3.9 billion in cash and marketable securities.

Saturday marks the eight-year anniversary of the site’s launch. The company has grown to attract 845 million monthly active users, including 425 million mobile monthly active users. The company identified mobile growth, competing products, dependency on Zynga, government censorship and negative media coverage among the challenges it faces moving forward.

Founder and CEO Mark Zuckerberg explained in a letter to investors that Facebook was not originally created to be a company, but to “accomplish a social mission.” He writes, “People sharing more — even if just with their close friends or families — creates a more open culture and leads to a better understanding of the lives and perspectives of others [...] We think a more open and connected world will help create a stronger economy with more authentic businesses that build better products and services.”

As we previously reported, the social network chose Morgan Stanley as the lead underwriter. Goldman Sachs, JP Morgan, Barclays Capital, Bank of America Merrill Lynch and Allan & Co. are also participating in the sale. It may be several months before Facebook debuts on the public market depending on broad market conditions and how company executives manage the Securities and Exchange Commission’s mandatory “quiet period.” The company cannot make any statements that might artificially inflate the value of its stock.

The filing comes at a critical time for Facebook. Private companies with 500 or more investors must legally make their financial records public within 120 days after the end of that calendar year. The social network did not have to make a public offering, but like Google which was in a similar position, it decided to go forward with an IPO anyway.