Google Inc., taking aim at Microsoft Corp.'s lucrative Office franchise, plans to release a free tool allowing users to transfer files from the widely used software suite to the Web so that multiple people can edit and collaborate on them.

The long-anticipated move is intended to bolster one of Google's fastest-growing businesses not related to its popular search engine--selling online software to companies. The company's Google Apps offering includes online word-processing, spreadsheet and collaboration tools used through...