Nope, a regular sword probably wouldn't do anything against that kind of armour (which is called plate armour, among other things). Arrows and crossbow bolts might have been able to poke a hole in it, but maybe not always. Once people started wearing plate armour, they had to come up with better weapons too, like a poleaxe or a halberd, or a "war hammer" or any other kind of heavy spiked club. Those kinds of weapons could penetrate the armour, but even if they didn't, they could knock a knight down or knock him right out.

Not everybody would be wearing full suits of plate armour though, since they were extremely expensive. You may be thinking of the fanciest suits of armour where the person is covered head to toe, and sometimes a knight did go into battle dressed like that. But armour like that was also used for special ceremonies or formal occasions like jousting tournaments. It's almost like modern soldiers - they don't fight in their dress uniforms!

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I think any books about knights and armour will discuss this, but personally my favourite is "Arms and Armour of the Medieval Knight" by David Edge and John Miles Paddock.