Filling in gaps in a PDF scan

[Sparrow]

This is just a small tip, but I'm finding it very helpful just now.

I'm converting a public domain PDF to text and am coming across some gaps where there is a word or two missing.

I'm using the only complete PDF file I could find for this book, so I was trying to figure out where I could check for the words that were missing.
It turns out that you can search Google books for a phrase near the gap, the search results will return a text snippet from Google books that ordinarily are 'Snippet view' or 'No preview available'.
The text displayed in the search results contains the missing words from the PDF I'm using.