The stock is down 9.2% at $182.76 after closing the regular session 0.7% higher.
For the quarter ended July 31, the Santa Clara, Calif., company posted a loss of 22 cents a share against earnings of 7 cents in the year-earlier quarter.
On an adjusted basis, earnings were $1.47 a share compared with $1.34. Revenue climbed 22% to $805.8 million.
Analysts surveyed by FactSet were expecting the company to report adjusted earnings of $1.42 a share on revenue of $802.4 million.
Fourth quarter billings also grew 22%, to $1.1 billion.
The company also said Wednesday that it definitively agreed to acquire an internet-of-things-security company, Zingbox, for $75 million. The deal is expected to close in the current quarter.
Palo Alto Networks is a key holding in Jim Cramer's Action Alerts PLUS charitable trust.