I know that once I start selling the app and it is out in the open I can't apply for a patent. I now also see there are various stages in the application process: file, search and examination.
At what point is the process started so that once I start selling I don't invalidate my own patent?
To obtain a patent, the invention should not be available in the public domain prior to filing a patent application.
However, the scenario is different in USA, in United states one can file for a patent within 1 year grace period after the invention has been disclosed in the public domain.
Secondly, one can sell an app immediately once it is filed. Although there are various stages involved for granting a patent, but this stages do not restrict for commercial exploitation of the app. It shall be noted that a commercializing the app after filing will not act as a prior art to invalidate the patent application.
http://www.invntree.com/blogs/which-stage-should-i-apply-patent
The rules are different for the U.S. and almost everywhere else. In the rest of the world when a patent is applied for the claimed subject matter needs to be new compared to whatever has been known the the public. In the U.S. we have a one year grace period before your own work can be used against you. If you file in the U.S. and then disclose, you can still file a foreign application if it is done within a year. Regarding dates - only the filing date matters.
