Stocks making the biggest moves premarket: Walmart, Slack, WPP, SAP, J&J, Roku & more
Check out the companies making headlines before the bell:

Walmart – Walmart U.S. stores chief Greg Foran will leave the retailer on Jan. 31 to become chief executive officer of Air New Zealand. He will be replaced by John Furner, who runs Walmart's Sam's Club warehouse chain.

Slack Technologies – Slack said it had more than 12 million active daily users during September, up 37% from a year ago. The workplace messaging company also said it had more than 6 million paid seats during the month.

WPP , Omnicom – The ad giants are among U.S.-traded advertising stocks that could be impacted today after French rival Publicis cut its full-year sales outlook.

Ford – Ford said China sales fell 30% during the third quarter, with the automaker delivering about 131,000 vehicles from July through September. Ford's China sales had fallen by about 36% in the first quarter and about 22% in the second quarter.

SAP — Chief Executive Officer Bill McDermott is stepping down, with Jennifer Morgan and Christian Klein taking over as co-CEOs of the enterprise software giant. The announcement came as SAP was reporting better-than-expected quarterly results.

Deckers Outdoor – Deckers was upgraded to "buy" from "hold" at Stifel Nicolaus, which said the footwear maker's product mix now gives the company protection from weather-related volatility.

Roku – Roku was upgraded by RBC Capital to "outperform" from "sector perform." RBC points to compelling valuation following a 31% decline in the streaming video device maker's stock, as well as strong fundamentals and favorable positioning.

Johnson & Johnson – Bernstein upgraded J&J to "outperform" from "market perform," saying the worst-case scenario regarding legal liabilities is now priced in, and that the valuation is "historically cheap."

Fastenal – The maker of construction and industrial supplies reported quarterly profit of 37 cents per share, 2 cents a share above estimates. Revenue came in slightly above Wall Street forecasts. Fastenal's results were helped by higher unit sales, as well as higher prices that had been implemented to mitigate the impacts of general and tariff-related inflation.

The Trade Desk – The provider of programmatic advertising technology was upgraded to "outperform" from "sector perform" at RBC Capital, based on a compelling valuation following a 32% decline, as well as strong fundamentals.