Exhibit 99.1

FOR IMMEDIATE RELEASE

For: Authentidate Holding Corp.

Investor Contacts:

Robert Schatz

Wolfe Axelrod Weinberger Assoc. LLC

(212) 370-4500; (212) 370-4505 fax

Authentidate Holding Corp. Announces

Conversion of Series C Preferred Stock into Common Stock

BERKELEY HEIGHTS, NJ – April 5, 2013 – Authentidate Holding Corp. (Nasdaq: ADAT), a provider of secure web-based software applications and telehealth products and services for healthcare organizations, today announced that at the company’s reconvened Special Meeting of Stockholders held on April 5, 2013, its stockholders approved the automatic conversion of the company’s outstanding shares of Series C 15% Convertible Redeemable Preferred Stock (the “Series C Preferred Stock”). The Series C Preferred Stock converted into an aggregate of 3,551,541 shares of common stock, including 1,051,541 shares of common stock issued in lieu of accrued but unpaid dividends on the Series C Preferred Stock. The shares of common stock issued upon conversion are subject to a six month restriction on transferability as described in the company’s supplement to its proxy statement for the Special Meeting dated March 22, 2013.

Ben Benjamin, Chief Executive Officer of Authentidate, stated, “We appreciate the continued support of our stockholders in voting to convert these securities into common stock. The conversion of these preferred securities strengthens our balance sheet, allows us to conserve resources and helps us to move forward aggressively with our growth plans.”

About Authentidate Holding Corp.

Authentidate Holding Corp. is a provider of secure web-based software applications and telehealth products and services that enable healthcare organizations to coordinate care for patients and enhance related administrative and clinical workflows. Authentidate’s products and services enable healthcare organizations to increase revenues, reduce costs and enhance patient care by eliminating paper and manual work steps from clinical and administrative processes. Authentidate’s telehealth solutions combine patient vital signs monitoring with a web application that streamlines patient care management. Delivered as Software as a Service (SaaS), customers only require an Internet connection and web browser to access our web-based applications thereby utilizing previous investments in systems and technology. The company’s healthcare customers and users include leading homecare companies, health systems, physician groups and governmental entities. These organizations utilize the company’s products and services to coordinate care for patients outside of acute-care.

For more information, visit the company’s website at www.authentidate.com

This press release contains forward-looking statements within the meaning of section 27A of the Securities Act of 1933 and section 21E of the Securities Act of 1934. When used in this release, the words “believe,” “anticipate,” “think,” “intend,” “plan,” “will be,” “expect,” and similar expressions identify such forward-looking statements. Such statements regarding future events and/or the future financial performance of the company are subject to certain risks and uncertainties, which could cause actual events or the actual future results of the company to differ materially from any forward-looking statement. Such risks and uncertainties include, among other things, the availability of any needed financing, the company’s ability to implement its business plan for various applications of its technologies, the impact of competition, the management of growth, and the other risks and uncertainties that may be detailed from time to time in the company’s reports filed with the Securities and Exchange Commission. In light of the significant risks and uncertainties inherent in the forward-looking statements included herein, the inclusion of such statements should not be regarded as a representation by the company or any other person that the objectives and plans of the company will be achieved.

Authentidate and Inscrybe are registered trademarks of Authentidate Holding Corp. All other trade names are the property of their respective owners.

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