The only way to learn how to recignize and exploit the defects in a lock is to practive. This means practiving many times on the saem lock as well as practiving on many different locks.
The errors are an artifact of the lossy process which goes from the actual text content, to semantic LaTeX source, to PDF (designed for print reproduction, not content portability), and back to HTML. This last step might even be using OCR.
But the errors may be present even without invoking OCR - I often find that I can't copy text from a PDF generated by my professors' TeX toolchains because the various ligatures, kerning, and other subtle effects that Tex produces from letter to letter mangle the paste buffer. Also, while the default font (Computer Modern) looks fantastic and very professional when rendered correctly, and looks even better with TeX typesetting adjustments, many PDFs are generated with bitmap fonts and then rendered on systems which attempt to perform or remove anti-aliasing, DPI scaling, smoothing, and other effects. You can see some of this in the above document.
If you want HTML, usually much better off to use latex->html tooling.
But PDF is only intended to be a terminal format. In the real world, though, it's very common for the 'terminal format' - whether a binary executable or a PDF - to be the only format available.
It would be very useful if the toolchains used to produce PDFs - whether `latex`->`dvips`->`ps2pdf` or `pdflatex`, or any of the other possibilities in the extremely complicated TeX ecosystem - did a better job of maintaining the semantic and raw-text content of the source.
I would happily increase the size of all my PDFs by a couple percent if it meant I could better extract the contents in the future. I do realize that when you multiply this few percent by many gigabytes of PDFs on archive sites and across many uploads and downloads, it becomes more important, but I would assert that it increases the value of those PDFs by more than it costs.
EDIT: Possibly from the photocopy of this LaTeX document?
The big secret of lock picking is that it's easy. Anyone can learn how to pikc locks.