It is impossible to get a patent based on a Provisional Patent Application. The utility patent application needs to be filed, which will then be examined and issued. This can be done in two ways without losing the benefit of your Provisional Application filing date:
Within one year of the Provisional filing date, file a regular US utility patent application or PCT International application and claim the Provisional advantage. A provisional application filing date will be transferred to the new application, giving the new application a priority filing date earlier but not reducing the 20-year term of the utility patent.
In order to proceed with the Utility Application, the Provisional Application must be converted. Even if the Provisional Application does not have claims, which are required in Utility Applications, the American Inventor’s Protection Act of 1999 (AIPA) allows a Provisional Application to be converted into a Utility Application. There appears to be no expectation that this route would be taken by the PTO, but it was added to deal with concerns in other countries that the Provisional would not be considered a “real” patent application for priority purposes. If the nonprovisional fee or declaration are not filed with the provisional application (which, of course, they would not have been), a surcharge will apply. Preliminary amendments were necessary if claims were not present in the provisional at the time of filing.
In the end, it shouldn’t matter which route you choose – filing a new application or converting the Provisional – but there might be a significant difference in the process.
It is normal to file a new application (claiming benefit from the Provisional) which is much more formal and, in most cases, much more detailed than the Provisional. A Provisional Application typically needs a lot of work to become a useful utility application, which is easier to do by filing a new application than by amending the existing one. Utility applications will be granted patents for twenty years, not the provisional filing date, from their actual filing date.
The usual rules against adding “new matter” to an existing application would apply if you converted the provisional into a non-provisional, so anything not contained in the provisional would not be allowed to be added. If a provisional is followed by a utility application, the “new matter” rules don’t apply, though the priority date does not apply to anything that was not in the provisional. In addition, there are additional forms to file – the petition to convert (with the surcharge for not paying the nonprovisional fee), the preliminary amendment to add claims, and all the additional transmittals. – which are not needed when a new application claims priority. The patent term is calculated from the filing date of the provisional (now non-provisional) application, not from the filing date of the later-filed utility application – so you lose up to a year of patent term.
As a result, conversion does not appear to have any advantages and has significant disadvantages. Specifically, the regulations permit the conversion and state that it is likely that you should file a new application in which you claim the provisional’s benefits. Although the conversion path is theoretically open, it is unlikely to be used practically.