make git ignore the timestamp embedded in PDFs

Question

How can I make git ignore the time stamp(s) in a PDF. Two PDFs that
differ only in these time stamps should be considered identical.

Here is an example:
,----
| > pdfinfo some.pdf
| Title: R Graphics Output
| Creator: R
| Producer: R 2.15.1
| CreationDate: Thu Jan 24 13:43:31 2013 "$TMPFILE"
|
| ## update the pdf metadata
| pdftk "$FILENAME" update_info "$TMPFILE" output "$TMPFILE2"
|
| ## overwrite the original pdf
| mv -f "$TMPFILE2" "$FILENAME"
|
| ## clean up
| rm -f "$TMPFILE"
| rm -f "$TMPFILE2"
| if [ -n $FILEASARG ] ; then
| cat "$FILENAME"
| fi
`----

This 'works' as far as the committed pdf indeed has the date reset to my default value.

However, when I re-checkout the files, they are marked modified by git.

So, my question is: How can I make git *completely* ignore the embedded date in the PDF?

Answer 1

I'm using cleaned files every now and then, but not on Linux. I have
never observed this behaviour recently.

If you 'git add' the file, does it keep its modified state? Does 'git
diff' tell a difference?