ReportLab - Metadata, CreationDate and ModificationDate - python-3.x

Question

How can I change metadata fields, CreationDate and ModificationDate, when I create a pdf with Reportlab?

Answer 1

Take a look at where modification and creation dates are set:
D['ModDate'] = D["CreationDate"] = \
Date(ts=document._timeStamp,dateFormatter=self._dateFormatter)
# ...
return PDFDictionary(D).format(document)
Basically, metadata is a dictionary saved at the end of binary string, start of string is file contents (document).
Inside Reportlab the workflow you ask about can be:
create canvas
draw something on it
get document from canvas
create PDFDictionary with artificial mod and create dates
format document with PDFDictionary
save to file
Change metadata of pdf file with pypdf also attempts similar goal.

Answer 2

The ReportLab (currently 3.5) Canvas provides public methods, like Canvas.setAuthor(), to set the /Author, /Title, and other metadata fields (called "Internal File Annotations" in the docs, section 4.5).
However, there is no method for overriding the /CreationDate or /ModDate.
If you only need to change the formatting of the dates, you can simply use the Canvas.setDateFormatter() method.
The methods described above modify a PDFInfo object, as can be seen in the source, but this is part of a private PDFDocument (as in Canvas._doc.info).
If you really do need to override the dates, you could either hack into the private parts of the canvas, or just search the content of the resulting file object for /CreationDate (...) and /ModDate (...), and replace the value between brackets.
Here's a quick-and-dirty example that does just that:
import io
import re
from reportlab.pdfgen import canvas
# write a pdf in a file-like object
file_like_obj = io.BytesIO()
p = canvas.Canvas(file_like_obj)
# set some metadata
p.setAuthor('djvg')
# ... add some content here ...
p.save()
# replace the /CreationDate (similar for /ModDate )
pdf_bytes = file_like_obj.getvalue()
pdf_bytes = re.sub(b'/CreationDate (\w*)', b'/CreationDate (D:19700101010203+01)', pdf_bytes)
# write to actual file
with open('test.pdf', 'wb') as pdf:
pdf.write(pdf_bytes)
The example above just illustrates the principle. Obviously one could use fancy regular expressions with lookaround etc.
From the pdf spec:
Date values used in a PDF shall conform to a standard date format, which closely follows that of the international standard ASN.1 (Abstract Syntax Notation One), defined in ISO/IEC 8824. A date shall be a text string of the form
( D : YYYYMMDDHHmmSSOHH' mm )