In short, a provisional patent application is a placeholder.  Provisional patent applications are never examined.  They never issue as enforceable documents.  Instead, they preserve for one (1) year your rights in whatever they disclose.  With the filing of a provisional application, you are legally entitled to designate the corresponding invention as “Patent Pending.”

To preserve patent-pending status and pursue patent protection claiming priority (i.e., back in time) to a provisional patent application, the provisional patent application must be converted to a “non-provisional” patent application before the one year anniversary.  If a provisional patent application expires without being converted, the rights it preserved cannot be extended.  Depending on the facts of your situation, this may forfeit certain patent rights.