[Python] Bolding existing text on a PDF while maintaining formatting in Python

I'm trying to recreate a Chrome extension called Bionic Reading that does not work on downloaded PDF files myself. Essentially, I'd like to bold the first few letters of every word on a PDF while keeping (roughly) the existing formatting & images. I've tried to utilize pypdf and ReportLab for this, but neither seems to provide the functionality I'm looking for. Any ideas?

I was able to bold the text of each word, but I wasn't able to simply edit the same PDF (or make a copy and edit that), but rather just copy the text and alter it. Formatting proved to be the main issue, as well as image retention (I'm hoping to use this to read research papers, so formatting and figures are very important).

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