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From "Jeremias Maerki (JIRA)" <>
Subject [jira] Commented: (FOR-1077) new CreationDate causes constant differences in output pdf documents
Date Wed, 05 Mar 2008 08:19:52 GMT


Jeremias Maerki commented on FOR-1077:

I'm pretty sure it's not only the XMP packet that has triggered this. It's not just the creation
date that changes each time a PDF is generated. The "ID" trailer element is generated from
the current date & time as per recommendation in the PDF specification.

Furthermore, even if the creation date is set in the XMP packet, it is explicitely not taken
into account when the PDF is generated. This is a merge rule for XMP data.

So how to go about this:
Ideally, Forrest would only recreate the PDF if the source file was actually changed but that's
probably unrealistic. So let's look at FOP: The "ID" element is actually optional but was
introduced because PDF/A functionality requires it. It would be easy to enable the "ID" element
only if PDF/A is enabled. Handling XMP metadata is more complicated. Even if you don't supply
an XMP packet in fo:declarations, some minimal XMP metadata is generated. And the XMP metadata
is synchronized with the legacy "Info" object in the PDF which also contains the creation

The only way I see is that some sort of special profile (like the PDF/A and PDF/X profiles)
is created that would skip the elements that change every time the PDF is generated. That
would take quite a bit of work though. And it would have to be enabled in Forrest/Cocoon somehow
once it's available.

> new CreationDate causes constant differences in output pdf documents
> --------------------------------------------------------------------
>                 Key: FOR-1077
>                 URL:
>             Project: Forrest
>          Issue Type: Bug
>          Components: Plugin: output.pdf
>    Affects Versions: 0.9-dev
>            Reporter: David Crossley
>             Fix For: 0.9-dev
> A problem has recently occurred with generating PDFs and publishing them. See the massive
amount of commits to the Forrest "site" svn today when two different committers updated the
website. Every PDF changed. I did some investigation and can see that a CreationDate is being
added. This is of course is changing on every run of forrest.

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