Commercial or open source? PDFTron can do it, but they’re not an open source project.
The goal is to draw a box using GUI, then use those coordinates to extract text from several homogeneous pages.
I also have a different goal of trying to interpret structure of a PDF that has visual structure (headers, sections and subsections all numbered). But that seems to lend itself to some sort of text parsing.
Some reading here: https://stackoverflow.com/questions/53219016/detecting-secti...
Here's how to extract text from a PDF based on coordinates (this explains how to do it on web, but it's also possible using other platforms):
https://groups.google.com/d/msg/pdfnet-webviewer/h2W3VksbQUI...
Here's how to extract a PDF's logical structure:
https://www.pdftron.com/documentation/samples/#logicalstruct...