Lightroom can be set to write the changes in meta data (including key words) to xmp file that will/should sit in in the same folder as your images and the key words should be searchable. If you do not set lightroom to do it they will only be stored in lightrooms catalog. Some lightroom experts maintain that Adobe should have this setting on by default.
https://helpx.adobe.com/lightroom/he...s-actions.html
https://helpx.adobe.com/lightroom/he...in_the_catalog