LANHAM, MD: PRWeb, an online news distribution service from Vocus, has added four distribution partners. Docstoc, an online community to find and share professional documents, will host PRWeb news releases in PDF format. State Newslines, a portfolio of localized Web properties, will carry a full range of PRWeb news. Trusted Earned Travel will feature PRWeb's travel-oriented press releases. And Visibility, an online marketing site, will carry PRWeb's SEO and online marketing-related releases.