Best time to ask if a search was good/bad

We have a internal document system where call center people search in real time while on calls for some specific files, or more accurately some information in the files. After the user clicks to the document to get the info they searched for we are wondering what might be the best way to ask if the file was helpful or not. Just a simple thumbs up or thumbs down. Wondering if there is a best practice to elicit this feedback while in the flow.