May I take my Paris car rental to Italy

We have done that twice, most recently in 2014.

Generally, yes but depending on the type of car it can be forbidden. Read the details to find Geographic restrictions. You may have to go to the rental car website to find the rules related to your confirmation number. The rules vary a lot among rental companies, time of year and type of car.

Most major car companies in Europe have few restrictions on taking their cars out of the country where you pick it up. Some have rules about taking them to certain countries in eastern Europe (such as the Czech Republic) but I can't imagine Italy being a problem.
Call the company and ask! If you can't do this then make sure you let them know at the rental counter when you pick up the car. They generally ask if you plan to take the car outside of the country. Many of them charge a fee for doing this but it isn't too much. I think I paid 35 euros extra last summer for taking a rental car out of the the Czech Republic and driving it through Hungary, Austria and Germany.

as others have noted, it depends on your specific rental company and rental agreement. Some allow, some don't. You'll have to read the fine print!

FYI, I was checking my car reservation for Amsterdam today and there is this rule:

• "DRIVING RESTRICTIONS: Vehicles may be driven throughout the countries of the Netherlands, Belgium, and Germany only."

So read the fine print provided by the rental agency not just the booking agent. To find this rule I had to take the confirmation number from Expedia and go to the Thrifty website to lookup my reservation and find the "rules and regulations" section, it was not mentioned on the Expedia website or the rental agreement.

I have done this many times and have always made the phone call to make sure my car could go to specific countries. Italy is sometimes a problem, but it depends on your rental company. I usually go with a major company but I do confirm with them. Also, there is some insurance that omits ceertain countries. I get the Amex insurance and seem to remember an occasional omission.

Just make sure with the car rental company that it will be ok. There are certain countries that are more problematic, not sure why? We used AutoEurope and talked with someone over the phone while making our plans. We had to rent from a specific agency (Hertz) to drive into Slovenia. It was not the most convenient rental location, but we had to go with them so we could drive into Slovenia. It was fine. Other times we have driven a German car into Austria, Italy, Switzerland etc. with no issues. But, just double check with the rental company.