Parse PDF shape data in python

I am trying to put together a script to fix PDFs a large number of PDFs that have been exported from Autocad via their DWG2PDF print driver.

When using this driver all SHX fonts are rendered as shape data instead of text data, they do however have a comment inserted into the PDF at the expected location with the expected text.

So far in my script I have got it to run through the PDF and insert hidden text on top of each section, with the text squashed to the size of the comment, this gets me 90% of the way and gives me a document that is searchable.

Unfortunately the sizing of the comment regions is relatively course (integer based) which makes it difficult to accurately determine the orientation of short text, and results in uneven sized boxes around text.

What I would like to be able to do is parse through the shape data in the PDF, collect anything within the bounds of the comment, and then determine a smaller and more accurate bounding box. However all the information I can find is by people trying to parse through text data, and I haven't been able to find anything at all in terms of shape data.

The below image is an example of the raw text in the PDF, the second image shows the comment bounding box in blue, with the red text being what I am setting to hidden to make the document searchable, and copy/paste able. I can get things a little better by shrinking the box by a fixed margin, but with small text items the low resolution of the comment box coordinate data messes things up.

To get this far I am using a combination of PyPDF2 and reportlab, but am open to moving to different libraries.

I didn't end up finding a solution with PyPDF2, I was able to find an easy way to iterate over shape data in pdfminer.six, but then couldn't find a nice way in pdfminer to extract annotation data.

As such I am using one library to get the annotations, one to look at the shape data, and last of all a third library to add the hidden text on the new pdf. It runs pretty slowly as sheet complexity increases but is giving me good enough results, see image below where the rough green borders as found in the annotations are shrunk to the blue borders surrounding the text. Of course I don't draw the boundaries, and use invisible text for the actual program output, giving pretty good selectable/searchable text.

If anyone is interested in looping over the shape data in PDFs the below snippet should get you started.

from pdfminer.high_level import extract_pages
from pdfminer.layout import LTLine, LTCurve

for page_layout in extract_pages("TestSchem.pdf"):
    for element in page_layout:
        if isinstance(element, LTCurve) or isinstance(element, LTLine):
            print(element.bbox)