Hi,
As with pavila, you were searching in the wrong category that is why your search did not return a result.
As for your next question, you can not change the keywords in your personal folder if you are logged in as user. You need to log in as system and view the repository and from there go to okm:home, then to the [OKM:FOLDER]user1, then okm:personal, then the file [OKM:DOCUMENT]file.doc, then click on edit in okm:keywords : (STRING) - Edit, and enter the keyword of your choice and press send. You can then close the repository view and search your keyword. It is not shown in the properties but it is already searchable by that keyword.
On the other hand, under taxonomy, if you have write access to a document you can change its keyword directly on the interface.
Thanks.