[poppler] getting the text from PDF files

[Leonard Rosenthol]

There are many different ways to add OCR’d text to a PDF, though one of the most common is use of “hidden text”, where the text is drawn using Text Render Mode 3.  I don’t recall if Poppler exposes this information in the public APIs, but it certainly has it in the graphic state internally.

Leonard

From: poppler <poppler-bounces at lists.freedesktop.org> on behalf of Stéphane Charette <stephanecharette at gmail.com>
Date: Friday, October 14, 2022 at 2:54 PM
To: poppler at lists.freedesktop.org <poppler at lists.freedesktop.org>
Subject: [poppler] getting the text from PDF files

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Using libpoppler-cpp-dev 0.86.1 on Ubuntu to read PDF files.  Works well.

doc->create_page(idx) to get the page, then page->text_list() to get all the boxes.  PDFs seem to either have text, or if it was a scan then I have an image with no text, and I fall back to other techniques to read what I need.

But...!  Some fax machines and business scanners try to do OCR, and embeds the text results into the PDF.  The quality of the OCR is poor, but when I attempt to extract the text, I do get back the expected text boxes which leads me down the wrong path.

Is there anything in the way the text was added to the PDF that I can use as a hint that the text was added to the PDF after-the-fact, and not as part of the original PDF creation process?  Something I can use to determine if the text can be trusted?  Reading up on things like Xref tables to get an understanding of the internals of PDF files so I can attempt to find a pattern between my "good" and "problematic" PDF files.  Wondered if there was a way to see if the text is part of the page itself, or if it was tacked on afterwards.

Thanks,

Stéphane

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Stéphane Charette
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