Can I use personal credit cards for business use?

yes but not a good idea

Yes, but that makes bookkeeping for your business more tangled up. 

Sure. Your employer may have a policy as to whether or not they will reimburse business expenses that you put on a personal card, so you’ll want to investigate that before doing so. If you happen to be your own employer, it will be a pretty quick investigation.

Lots of people do. If you want reimbursement it might depend on your company and your records.

I did for years. My own business. Business credit cards have fewer fraud protections so I never wanted one..

If this is your business then yes. Assuming you want to claim things as business expenses, then keep really good records so you can account for them come tax time.  Your other concern is making sure you get reimbursed properly from the company.  Especially if you're registered as a corporation you want to keep your personal finances separate from your business finances.  If you don't, then someone could sue you directly for things the company does since you're not acting as a proper corporation.

If it's not your business, then that is the company you work for's policy.  My experience is for most things it is fine to use one and turn in the proper expense report to get reimbursed.  You should check with your company's policies however.

Yes