Patents are available only for inventions that are new and by definition an invention cannot be new if it is already known to the public.
If you want a patent for an invention be very careful who you tell. An example of what can go wrong is poor old Dr Palmaz who gave
"a short presentation of 5 to 10 minutes, perhaps 8 minutes, to about 40 members of the Radiological Society of North America. He accepted that it was a public disclosure and that at the meeting he showed slides, one of which showed the drawings depicted ...... "
That was enough for a judge to find disclosure of the invention and the Court of Appeal could not reverse it (see Boston Scientific Ltd v Palmaz  EWCA Civ 83 (20 March 2000)). Accordingly, the invention was not patentable.
What do you do about it? The Patent Office has published some useful stuff in its leaflet entitled "Confidentiality and Confidential Disclosure Documents". It has to be stressed that many people don't like signing confidentiality agreements for very good reasons. That is particularly the case with big companies who are offered an unsolicited idea from a member of the public. One reason they may decline to sign such an agreement is that they are already working on similar projects and don't want to be accused of nicking other peoples' ideas. Another is that it is often unnecessary for a decision on whether to accept the unsolicited offer. What they need to know is whether an invention will fit into their business and as often as not they can decide that without knowing how to make the invention.
Remember also that getting the other side to sign a confidentiality agreement is never enough in itself. You need to monitor and enforce disclosures of trade or business secrets. For example, make a note of the date, time, place and persons present at the conversation at which information was disclosed and set out clearly in the record a summary of the subject matter of the disclosure. Similarly, record the date, time and place of delivery of a document and make sure that it is handed back when it is finished with.
Confidential info is a complex area of the law and you may need professional help. For more on the law see "Confidential Information" on our IP/it-Update site. For a case study and more on what can be done visit "Confidential Information" on the nipc site.