UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D. C. 20549

FORM 10-K/A

Commission File Number: 000-18908

PREVIEW SYSTEMS, INC.
(Exact name of registrant as specified in its charter)

Registrant's telephone number, including area code: 408-720-3500

Securities registered pursuant to Section 12(b) of the Act: None

Securities registered pursuant to Section 12(g) of the Act: Common Stock, $.0002 par value

    Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days:  Yes /x/  No / /

    Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of Registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K, or any amendment to this Form 10-K.  /x/

    The aggregate market value of the voting stock held by non-affiliates of the Registrant is $737,316,577 as of March 10, 2000 based upon the last sales price as reported by the Nasdaq National Market System.

    The number of shares outstanding of the Registrant's Common Stock as of March 10, 2000 was 16,785,882 shares.

    The Registrant hereby amends the following section included in Item 1 of its Form 10-K for the fiscal year ended December 31, 1999 filed with the Securities and Exchange Commission on March 30, 2000:

PART I

ITEM 1. Business

    Risk Factor—Substantial sales of our common stock could depress our stock price.

    If our stockholders sell substantial amounts of our common stock in the public market, the market price of our common stock could fall. Based on 16,785,882 shares outstanding as of March 10, 2000, we had 4,395,912 shares of common stock eligible for sale in the public market. The remaining shares of common stock outstanding are subject to lock-up agreements that prohibit the sale of shares for 180 days from the date of our initial public offering (December 8, 1999). Immediately after the 180 day lock-up period, the remaining outstanding shares of our common stock will become available for sale in the public market, except in the case of 4,797,199 shares which are subject to the expiration of one-year holding periods and/or the lapse of our repurchase options.

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SIGNATURES

    Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

    Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the Registrant and in the capacities indicated on May 12, 2000:

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QuickLinks

ITEM 1. Business