Step 1: Convert the PDF into one which has (nearly) all PDF objects' contents and streams expanded into a readable form using QPDF.
qpdf --qdf --object-streams=disable input.pdf output.pdf
Step 2: Open using an text editor and replace all instances of the keyword 'font' with anything really.
Step 3: ???
Step 4: Profit
NB: Modify the 'TJ' tags of the stream objects to remove specific texts.