Subtext, an expansive ebook service, has raised $3m in financing from investors including Google Ventures.

US-based digital reading startup Subtext revealed on Tuesday that it had raised $3m in seed funding from corporate venturing unit Google Ventures, venture capital firms The Mayfield Fund and New Enterprise Associates, and philanthropic investment firm Omidyar Network.

The investment was disclosed as Subtext launched its first product, a free application for the iPad. Subtext develops social networking and expansion features for ebooks which link readers to additional content based around the book, and its bookshelf is compatible with…