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Don’t file a napkin provisional.
A “napkin provisional” is a short description of an idea, filed as a provisional patent application, with little more than a cover sheet to support it. The first patent that you file on your product is the foundation upon which your patent house is built.
Don’t build your house on sand.
Do it right. Do a search. Then figure out whether (and if so, how) to file.
Sometimes it makes sense to file a provisional patent application (instead of a utility patent application) in order to get an extra year of “patent pending” status. This is especially true for software, in light of recent court decisions and USPTO guidelines (issued 2014-12-15) for software (http://www.uspto.gov/blog/director/entry/guidance_on_subject_matter_eligibility).