Finding (and re-finding) locations in text documents is a common activity for most computer users -- but tools for document navigation are still limited in many ways. Previous research has shown that a spatially-stable overview of the entire document can be substantially faster than any other navigation technique -- particularly when revisiting previous locations. However, the overview technique has only been tested in a limited laboratory study, so little is known about whether it works in more realistic contexts. To answer this question, we developed a PDF viewer that incorporates several document-navigation techniques, and carried out two studies. First, we ran a field experiment in which users carried out search tasks using an overview and other techniques -- on their own computers in a non-laboratory environment. Second, we ran a smaller field study in which people used our viewer (with choice of navigation techniques) for their own PDF tasks. In the field experiment, the overview was significantly and substantially faster than other techniques, and in the field study, the technique was frequently used for a wide variety of documents. Our work provides confirmation of the value of spatially stable overviews as a basis for document navigation.