ID added to pdf metadata - what is it good for?

[charlesleroi]

Hi everybody.

I used exiftool to change some pdf's metadata. I noticed that after editing the metadata, an ID was added to every pdf's metadata. This ID is the same for every edited pdf.
What's the purpose of this ID?

This ID is not shown when reading the metadata with exiftool. But when I had an additional look on the metadata with mat2 this ID was displayed.

The pdf's metadata looks like this:
author: ...
creation-date: ...
creator: ...
pdf-format: ...
metadata: <?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d ...


Kind regards,
Charles

[Phil Harvey]

Hi Charles,

That is the XMP metadata packet.  The ID is just the XMP record ID.

You will get this if you add any XMP tags to any file.

- Phil