The Bluebook requires citation to printed material (provided it is available), unless there is an authenticated, official, or exact digital copy of the printed sources. See R. 18.2.
Example: The Ohio Supreme Court has designated the Supreme Court website as the Ohio Official Reports for opinions of the courts of appeals and the Court of Claims. See Ohio Rep. Op. R. 3.2, http://www.supremecourt.ohio.gov/LegalResources/rules/reporting/Report.pdf. These opinions are in PDF format and bear a watermark.
If there is no print format or if the print format is obscure and is, for all practical purposes unavailable, cite to the most stable Internet source available.
Eric Goldman, When Should Search Engines Ignore Court Orders To Remove Search Results?,Tech. & Marketing L. Blog (Sept. 4, 2013), http://blog.ericgoldman.org/archives/2013/09/when_should_sea.htm.
Bill Ong Hing, Understanding SB1070 from the Lens of Institutionalized Racism and Civil Rights, Legal Services N. Cal., http://www.equity.lsnc.net/understanding-sb1070-from-the-lens-of-institutionalized-racism-and-civil-rights (last visited Sept. 5, 2013).
A parallel citation to an Internet source may be provided if it substantially improves access to the source. Follow the regular rules for citing the source and then add the parallel Internet citation.
Commission on Women in the Profession, American Bar Association, From Visible Invisibility to Visibly Successful: Success Strategies for Law Firms and Women of Color in Law Firms (2008), available at http://www.americanbar.org/content/dam/aba/migrated/women/woc/VisiblySuccessful.authcheckdam.pdf.
D. Andrew Austin & Mindy R. Levit, Cong. Research Serv., The Debt Limit: History and Recent Increases (Aug. 27, 2013), available at http://fpc.state.gov/documents/organization/213995.pdf.
Haw. Rev. Stat. § 201-1 (date), available at http://www.capitol.hawaii.gov/hrscurrent/Vol04_Ch0201-0257/HRS0201/HRS_0201-0001.htm.
Traton News, L.L.C. v. Traton Corp., No. 12-4139 (6th Cir. June 11, 2013), available at http://federal-circuits.vlex.com/vid/traton-news-llc-v-corp-440553998.