Can this be used to paint an adirondeck chair made out of pine?

Rust-Oleum Restore 10x Advanced is for use on horizontal surfaces only. This product will sag when applied to a vertical surface. It's also a very textured product. This may not be the most comfortable product for use on this type of surface. Instead, you may want to consider priming with Zinsser Bullseye 1-2-3 Water-Based Primer and Sealer and then use a top coat of your choice. https://www.lowes.com/pd/Zinsser-Bulls-Eye-1-2-3-Interior-Exterior-Latex-Primer-Actual-Net-Contents-128-fl-oz/3439970

Yes it can, but remember the texture is very rough and designed for decks.