So I've spent the good majority of a month on this issue. I'm looking for a way to extract geometry elements (polylines, text, arcs, etc.) from a vectorized PDF organised by the file's OCGs (Optional Content Groups), which are basically PDF layers. Using PDFminer I was able to extract geometry (LTCurves, LTTextBoxes, LTLines, etc.); using PyPDF2, I was able to view how many OCGs were in the PDF, though I was not able to access geometry associated with that OCG. There were a few hacky scripts I've seen and tried online that may have been able to solve this problem, but to no avail. I even resorted to opening the raw PDF data in a text editor and half hazardly removing parts of it to see if I could come up with some custom parsing technique to do this, but again to no avail. Adobe's PDF manual is minimal at best, so that was no help when I was attempting to create a parser. Does anyone know a solution to this. 
At this point, I'm open to a solution in any language, using any OS (though I would prefer a solution using Python 3 on Windows or Linux), as long as it is open source / free. 
Can anyone here help end this rabbit hole of darkness? Much appreciated!
A PDF document consists of two "types" of data. There is an object oriented "structure" to the document to divide it into pages, and carry meta data (like, for instance, there is this list of Optional Content Groups), and there is a stream oriented list of marking operators that actually "draw" content onto the page. 
The fact that there are OCG's, and their names, and a bit about them is stored on object oriented content, and can be extracted by parsing the object content fairly easily. But the membership of the OCG's is NOT stored in the object structure. It can only be found by parsing the Content Stream. A group of marking operators is a member of a particular OCG group when it is preceeded by the content operator /OC /optionacontentgroupname BDC and followed by the operator EMC.
Parsing a content stream is a less than trivial task. There are many tools out there that will do this for you. I would not, myself, attempt to build such a parser from scratch. There is little value in re-writing the wheel.
The complete syntax of PDF is available from many sources. Search the web for "PDF Specification 1.7", or "ISO32000-1:2008". It is a daunting document to read, but it does supply all of the information needed to create both and object and a content parser
Extract Geometry Elements from PDF by OCG (by Layer)