Advanced search within single document?

This may be a stupid question, but I can’t figure out how to conduct an advanced search (e.g. proximity) limited to a specific document, say a 100 page PDF. I know how to limit a search to a specific group via Search In (in Advanced Search) and In Selection (in the search bar). I know how to invoke the generic Mac search window (Ctl-F) within a single document, but this doesn’t use DT’s proximity or any other features. I know I could create a separate group for a single document. But is there a simple way to select a specific document (say in three pane view or in its own window) and then run a complicated search on it and only it?

Click the magnifying glass at the end of the searchField and choose “In Selection”.

Thanks for the quick response. I’ve tried that but it doesn’t seem to work. I select a specific record in 3-pane view, choose ‘Option-In selection’ under the magnifying glass, type my search in the box and I get multiple files in the results; the content view of the selected document remains the same, but no highlighted search terms. When I delete the search string in the search box I see ‘All/In Selection/Prefix’ in a gray font in the blank box, so the search box presumably knows I selected that option. What am I doing wrong?

You could temporarily put this file in its own group then select the group and do the search.