pdf.verify throws an UnicodeDecodeError on files modified with PyMuPDF

I experimented with PyMuPDF, endesive and some signed PDFs and noticed that endesive's verify function works on various modified PDFs at all (I first discovered it on PDF's with financial data, and then reproduced it on something generic as seen below) For example, using pdf-acrobat.pdf from endesive repo saved in the same directory as the script:

import pymupdf
doc = pymupdf.open('pdf-acrobat.pdf')
print(doc.get_sigflags())
page = doc[0]
rects = page.search_for("world")
page.add_highlight_annot(rects)
doc.save("output.pdf")

And then trying to verify it:

from endesive import pdf
data = open("output.pdf", "rb").read()
(hashok, signatureok, certok)= pdf.verify(data, None, None)
print("signature ok?", signatureok)
print("hash ok?", hashok)
print("cert ok?", certok)

Leaves a traceback:

UnicodeDecodeError                        Traceback (most recent call last)
Cell In[8], line 3
      1 from endesive import pdf
      2 data = open("output.pdf", "rb").read()
----> 3 (hashok, signatureok, certok)= pdf.verify(data, None, None)
      4 print("signature ok?", signatureok)
      5 print("hash ok?", hashok)

File ~/playground/.venv/lib/python3.12/site-packages/endesive/pdf/verify.py:14, in verify(pdfdata, certs, systemCertsPath)
     12 br = [int(i, 10) for i in pdfdata[start + 1 : stop].split()]
     13 contents = pdfdata[br[0] + br[1] + 1 : br[2] - 1]
---> 14 bcontents = bytes.fromhex(contents.decode("utf8"))
     15 data1 = pdfdata[br[0] : br[0] + br[1]]
     16 data2 = pdfdata[br[2] : br[2] + br[3]]

UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8e in position 0: invalid start byte

m32 / endesive

pdf.verify throws an UnicodeDecodeError on files modified with PyMuPDF #172