We presume that you wish to search for a Document (Invoice / Estimate etc) by typing in a text contained in the Notes section. If my understanding is correct, please note that it is not possible. You can check out the Advanced Search feature for the respective module to know more about the data with which the documents can be filtered.
Hope this should help.
If I haven't understood your query correctly, kindly feel free to write back to us. We would love to be of help.