PostScript function to embed files in a PDF easily using pdfmark (by defaults dumps /tmp/* ) (e.g. ```gs -sDEVICE=pdfwrite -o foo.pdf embedfile.ps```). Python script extracts the files.

embedfile.ps

%!PS

%%%%%%%%%%%%%%%%%%%Helper Functions

% (a) (b) -> (ab) 
/concatstrings { exch dup length 
 2 index length add string 
 dup dup 4 2 roll copy length
 4 -1 roll putinterval
} bind def

%https://comp.lang.postscript.narkive.com/lb2y58U5/string-replace-in-postscript
% comp.lang.postscript FAQ 7.8:
% string1 string2 *append* string
% Function: Concatenates two strings together.
/append {
	2 copy length exch length add % Find the length of the new.
	string dup % string1 string2 string string
	4 2 roll % string string string1 string2
	2 index 0 3 index % string string string1 string2 ...
	% ... string 0 string1
	putinterval % Stuff the first string in.
	% string string string1 string2
	exch length exch putinterval
} bind def


% replace string find *findandreplaceall* string'
/findandreplaceall {
	() 4 1 roll % string' is an empty string initially.
	{
		search { % string' replace post find pre
			3 index append 5 -1 roll % replace post find tail' string'
			exch append 4 1 roll % string' replace post find
		} {
			exch pop append
			exit
		} ifelse
	} loop
} bind def

%%%%%%%%%%%%%%%%%%%Actual code

% Embeds the file located at parameter 1 into the PDF
% https://ghostscript.com/blog/zugferd.html
/EmbedFile {
	/inputFileName exch def
	% As pdfmark does not support dynamically generated objname's, generate the code dynamically and replace the name with a dynamically generated one
	({) inputFileName concatstrings (Stream}) concatstrings (
		[ /_objdef {InvoiceStream} /type /stream /OBJ pdfmark 
		[ {InvoiceStream} << /Type /EmbeddedFile /Subtype (application/octet-stream) cvn >> /PUT pdfmark
		[ {InvoiceStream} inputFileName (r) file /PUT pdfmark 
		[ {InvoiceStream} /CLOSE pdfmark 
		[ /Name inputFileName /FS << 
			/Type /FileSpec 
			/F inputFileName
			/AFRelationship /Alternative
			/EF << /F {InvoiceStream} >>
		>> /EMBED pdfmark 
	) ({InvoiceStream}) findandreplaceall cvx exec
} def

(/tmp/*) { %filenameforall
    {
        EmbedFile
    } stopped {} {} ifelse
} 4096 string filenameforall

extract_pdf_attachments.py

# very slightly modified version of https://gist.github.com/kevinl95/29a9e18d474eb6e23372074deff2df38 with cmd arguments and by default no output 
import PyPDF2
import sys
from pathlib import Path

def getAttachments(reader):
    """
     Retrieves the file attachments of the PDF as a dictionary of file names
     and the file data as a bytestring.
      :return: dictionary of filenames and bytestrings
    """
    catalog = reader.trailer["/Root"]
    fileNames = catalog['/Names']['/EmbeddedFiles']['/Kids'][0].getObject()['/Names']
    attachments = {}
    for f in fileNames:
        if isinstance(f, str):
            name = f
            dataIndex = fileNames.index(f) + 1
            fDict = fileNames[dataIndex].getObject()
            fData = fDict['/EF']['/F'].getData()
            attachments[name] = fData
    return attachments


handler = open(sys.argv[1], 'rb')
reader = PyPDF2.PdfFileReader(handler)
dictionary = getAttachments(reader)

# print(dictionary)
for fName, fData in dictionary.items():
    path = Path.cwd() / ("." + str(Path(fName).resolve()))
    path.parent.mkdir(parents=True, exist_ok=True)
    with open(path, 'wb') as outfile:
        outfile.write(fData)