The simple answer is no. Neither does a regular patent application or an issued patent for that matter. Just like a deadbolt lock on your front door does not “protect” your house against theft. Instead, it serves as a deterrent. If someone really wants to rob your home, they are going to do it regardless of whether you have a deadbolt lock.
Now for the technical answer. A provisional patent application (and even a regular patent application) does not “protect” your invention. You can only enforce an issued patent against an alleged infringer of your invention. This is because a patent application has not been examined yet, and theoretically, you could file a patent application for anything, regardless of whether you are entitled to patent protection.
Once a patent application has been examined by the US Patent Office and the Examiner has determined that the invention is entitled to patent protection, the patent can be enforced against an alleged infringer.
Enforcing a patent against an infringer typically means a court action and patent litigation. If the court agrees that the alleged infringer is indeed infringing, the court may issue a court order requiring the infringer to stop infringing the patent. The court may also award money damages. If the infringer knew of the patent and infringed anyway, the patent owner may be awarded enhanced damages – for willful infringement.
While a patent application cannot be enforced, a patent application does offer”patent pending” status for the invention as soon as the application is filed with the US Patent Office. As such, the application should mark the product embodying the invention, and any advertisements, brochures, and other literature about the invention, as “Pat. Pend.” as soon as a patent application is filed for the invention.
Warning: Don’t mark your product as patent pending until a patent application has actually been filed – it is against the law to do so!
Legitimate businesses should at least investigate a claim of patent pending. That is not to say there won’t be those who copy your invention. This is true even for patented inventions. Just as there will always be people who rob houses even if there is a deadbolt lock on the house.