I have done something in a company, which has not been patented. Can I file a patent for the idea in another company?
Can I file a patent for the idea in another company?
Most probably not.
I suppose it has to do with your employment agreement, but the answer is almost certainly no you can't file for a patent on an idea generated during previous employment. For most people, your work product is owned by the company who is paying you. This has been true for me during my entire professional career both as a full time employee and as a consultant. When a company files a patent, the inventor is listed as such, but the assignee is the company who will own the patent (should it be granted). A company can decide to obtain a patent or not, but the decision not to doesn't change the fact that they control the idea and can decide to keep it trade secret or even publish the idea to keep others from patenting it. Indeed, just telling your new company about the idea might open you up a lawsuit if the idea is considered confidential information by your old employer. Please note that I am not a lawyer and this is not legal advice. Also, the law may differ based on where you are employed.