Edit to remove some info that did pertain to updating attachments.
You can give this a try:
from os import listdir
from os.path import isfile, join
import csv
import arcpy
fc = r'path to the attachments fc'
pdfDir = r'path to pdf directory'
# create a dictionary of pdf files.
pdffiles = {f: {'filePdf': f.split('.')[0], 'filePdfName': f, 'pdfPath': join(pdfDir, f)} for f in listdir(pdfDir) if all([isfile(join(pdfDir, f)), f.endswith('pdf')])}
# add the matching OBJECTID from the featureclass:
# make list of pdf names for the sql query.
pdfs = [k for k in pdffiles.keys()]
# limit the results to the pdfs in the folder and add the objectID to the dictionary.
sql = f"""attach_name IN ({str(pdfs)[1:-1]})"""
with arcpy.da.SearchCursor(fc, ['OBJECTID', 'attach_name'], sql) as sCur:
for row in sCur:
pdffiles[row[1]]['OBJECTID'] = row[0]
# convert the pdf file dict to a list of dicts containing the matched objectid and pdf data.
dict_data = [dict(v.items()) for k, v in pdffiles.items()]
# fields to use as the csv header
csv_header = ['OBJECTID', 'filePdf', 'filePdfName', 'pdfPath']
# write the csv
with open(r'match.csv', 'w', newline="") as csvfile:
writer = csv.DictWriter(csvfile, fieldnames=csv_header)
writer.writeheader()
for data in dict_data:
writer.writerow(data)
# add the attachments
arcpy.management.AddAttachments(fc, 'OBJECTID', 'match.csv', 'OBJECTID', 'pdfPath')
