UPDATE 1-Autodesk shares down on 4th-qtr forecast

(Recasts, adds acquisition, stock price, outlook)

LOS ANGELES Nov 15 (Reuters) - Autodesk Inc (ADSK.O) on Thursday posted a 47 percent jump in third-quarter profits but forecast lower-than-expected fourth-quarter earnings, sending its shares lower in after-hours trade.

Net income increased to $85 million, or 35 cents per share, from $58 million, or 24 cents per share, a year earlier.

It forecast fourth-quarter earnings, excluding items, to range from 52 cents to 54 cents, while analysts on average had forecast fourth-quarter earnings, before items, of 54 cents per share on revenues of $581.8 million, according to Reuters Estimates.

Shares of Autodesk fell 5.2 percent to $45 in after-hours trade, after closing down 7 cents to $47.46 a share on Nasdaq.

Autodesk, known for its AutoCAD design software, said revenues rose 18 percent to $538 million.

The company said it planned to buy Robobat, a privately held company based in Grenoble, France, that specializes in analysis, design, and steel and concrete detailing software for about $42.5 million in cash subject to a working capital adjustment.

It said the deal is expected to decrease targeted net earnings per share by 1 cent per share in both fiscal 2008 and fiscal 2009.

It also said that net revenues for the fourth quarter are expected to be between $575 million and $585 million, while earnings per diluted share are expected to be in the range of 42 cents to 44 cents per share. (Reporting by Sue Zeidler; Editing by Gary Hill)