How to compress signed documents

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pauldenize
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How to compress signed documents

Post by pauldenize »

Is their a way to compress digitally signed PDF Files please ?

Can someone advise how this can be done (or if it cant do it).
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TrackerSupp-Daniel
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Re: How to compress signed documents

Post by TrackerSupp-Daniel »

Hi, pauldenize

Unfortunately it is not possible to further compress a document after digitally signing. This is because signing generates a special validation key which can be used to ensure that none of the document data has been altered. In compressing the document (regardless of who or how it is done), you would be altering almost all of the existing data, and thus the signature would become invalid.

I suppose I should also note, though this is a different type of compression, it is possible to "Zip" a pdf document which has been signed to effectively "compress" the file.

Kind regards,
Dan McIntyre - Support Technician
Tracker Software Products (Canada) LTD

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PHK
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Re: How to compress signed documents

Post by PHK »

But if all you need is an image of the document with an image of the signature(s) on the document, you can flatten the document and save it, can't you? I do it "all the time."
All best,

FringePhil
Willy Van Nuffel
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Re: How to compress signed documents

Post by Willy Van Nuffel »

Hi PHK,

When you just add an image of your signature to the PDF document, it still has no legal value. Everyone can add a copy of a signature to a PDF-document and pretend he/she is the author of it. Recompressing such a document would have no influence.

Digitally Signed PDF's are validated by the PDF-software when they are opened.
At the time when the document has been signed and saved by the author (using an official digital signature delivered by a certificate authority like for example GlobalSign or VeriSign) there has been add a checksum (verification number) to it. As long as the content of the document has not been altered after it has been saved AND the digital signature can be validated against the Certificate Authority (CA), the PDF-reader will show the digital signature as being valid. So, the reader can be sure that the document is still authentic. When you should compress such a document after it has been signed, its authenticity would be broken.

Best regards.

Willy.
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PHK
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Re: How to compress signed documents

Post by PHK »

@ Willy. I fully accept all that you say.

We don't really know how the OP intends to use the files. However, if one just wants to have the "smallest" viewable image file of the document, I think my suggestion above works.
All best,

FringePhil
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Tracker Supp-Stefan
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Re: How to compress signed documents

Post by Tracker Supp-Stefan »

Hi All,

There were some links to a third party tool in the original post. Apparently with that tool it seemed like such an operation is possible, but is effectively breaking the signatures, so it's as if you compress a version of the file without the signatures in it and then adding them back invalidated. It's not something that we offer, but yeah if smallest possible file is desired - going through images might be a viable workaround.

Kind regards,
Stefan
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PHK
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Re: How to compress signed documents

Post by PHK »

Even if straight-forward unlayered document files may not have the verifiability of digitally signed virtual documents that some promoters (DocUSign, etc.) espouse, that does not mean that they are not admissible as evidence. Sure, their security chain is not as robust as perhaps others, but they would probably be better than nothing at all. Again, it all goes back to the user's real World requirements. But just because a documentation server application insists on high levels of verifiable originality does not mean that the downstream clients have to adhere to the same elevated standards.
All best,

FringePhil
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TrackerSupp-Daniel
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Re: How to compress signed documents

Post by TrackerSupp-Daniel »

Hi, PHK

That is true, but the original question specifically pertained to "digitally signed" files, and our answers here have thus pertained to that answer. Regardless of the use/intent or purpose, a digital signature, which innately contains self verification, would prevent a document from being compressed.

If a user does not need to place a verifiable digital signature, than simply using a stamp, or the "signatures and initials" tools would actually be a better option than rasterizing as you have suggested. As in most cases, having a few fonts, small images, and shapes would result in a smaller file than having a single large image. And as a bonus, since these methods do not place security on the file, they can often be further compressed.

Kind regards,
Dan McIntyre - Support Technician
Tracker Software Products (Canada) LTD

+++++++++++++++++++++++++++++++++++
Our Web site domain and email address has changed as of 26/10/2023.
https://www.pdf-xchange.com
Support@pdf-xchange.com
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