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https://issues.apache.org/jira/browse/FOR-1077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575264#action_12575264
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Jeremias Maerki commented on FOR-1077:
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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 date.
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: https://issues.apache.org/jira/browse/FOR-1077
> 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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