should you build PD AND Shiv on an adc?

Nope, Standard build if youre lacking damage or Build for Enemy Heavy AP teams or or Build for Enemy Heavy AD teams or or Basically find out whats doing damage to you and build a defensive item accordingly. Otherwise, Bork is always a better alternative because it does 8% of their CURRENT HEALTH on hit, which is insane. It provides you with peel, and gives you even more lifesteal. But typically you always want a defensive item. Also side note, build phantom dancer when you or your team is ahead, shiv for when you are behind. Shiv is better early game, PD is better late.

It's a tad excessive. You're better off grabbing one with infinity edge. Stacking crit and attack speed might seem like a great idea, but you need a mix of stats to be effective as an adc. Fortunately a lot of adc items tend to be cost and stat efficient to maximize your dps.

After you have six items as a boot replacement. But > . At full build not critting will cost you more damage than shiv proc does when it crits.

goes well together if you sell boots. Otherwise getting both is not really benefical you get more stat/g ratio with more AD.

I think Vayne is the only champion you can do that on. And, even then I'm not too sure, because I don't really play Vayne.

Double PD much better than PD Shiv. Sometimes if I'm really fed as Lucian I build PD on top of a Shiv that I bought before for crit and speed for ult. But yeah, better to go with double PD.