Inspiring

Question

Flattening PDF with digital signatures

Forum|Forum|6 years ago
September 15, 2019
7 replies
59905 views

Can someone explain to me what exactly is 'flattening' a PDF ? Is it done so a document can't be tampered with? Why would you need to flatten a PDF? For printing?

I was taught to save our documents by Printing to Adobe and told that was flattening, which I've learned now it is also referred to as 'refrying', not a practice supported by Adobe. The reason we were instructed to 'refry' was so the document could not be tampered with after we save it. We work with Acrobat so even Optimizing seems like a better alternative, although, I don't think either is necessary. Several digital signatures are applied to the document but can still be editted after they are applied. However, I've added a script on my particular form so it locks when the last signature is applied by the manager, which is how I save now. The other departments are still saving the document by refrying. As far as I understand, the final digital signature is enough by locking it so it can't be tampered with. The other departments don't lock after they are signed (for now at least) but I do not think flattening the PDF is necessary, am I correct? How can I explain that 'refrying' is not good practice? I kind of understand but I really need help expaining it.

This topic has been closed for replies.

JR Boulay

Community Expert

TBemrose you're confusing flattening and pixelating (which is not a good practice).

And also, I'm all alone in my head, so please don't refer to me as "they".

Acrobate du PDF, InDesigner et Photoshopographe

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TBemrose

Participant

I can add this: What Adobe calls "flatten" isn't truly flatten. It's flatten-ish. Every method I've ever found online to flatten a PDF, printing to file, etc., including any Adobe Pro feature with "flatten" in the name, never truly flattens the PDF.

False --> https://www.adobe.com/acrobat/hub/how-to-flatten-a-pdf.html

@abracadabraJRB alludes to this in their answer when they say "graphics objects". <---- Plural: "objectS". Not flattened. Take any PDF, add an image onto it (like a signature image for example). Apply any so called 'flatten' process, and you can still select the image and even save it externally (which then allows you to start applying that image to other documents - uh oh).

The only way I've found to truly flatten a PDF is to either export it as jpg (or take a screenshot) and then create a new PDF based on that image. Now you can't select that (added/signature) image separate from anything else on the page - everything has truly been flattened into the page / into a single layer.

Abambo

Community Expert

The only way I've found to truly flatten a PDF is to either export it as jpg (or take a screenshot) and then create a new PDF based on that image. Now you can't select that (added/signature) image separate from anything else on the page - everything has truly been flattened into the page / into a single layer.

By @TBemrose

I can. And depending on the placement of that, it is really easy. In a digital world, signatures should be digital, not graphic. It does not mind what you do, "flatten" or "pixelateing", the signatures will be unverifiable. 😉

ABAMBO | Hard- and Software Engineer | Photographer

ls_rbls

Community Expert

Please see slides below:

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traceyc28668387Author

Inspiring

So a fix to this is to change the trust settings.

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traceyc28668387Author

Inspiring

I can't seem to insert an image so I'll have to explain, ugh.

ls_rbls

Community Expert

https://helpx.adobe.com/story/help/track-changes-settings.html <<-------- how to see changes made in a document

https://helpx.adobe.com/acrobat/using/validating-digital-signatures.html <<--------how to validate sigantures applied in a document

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traceyc28668387Author

Inspiring

So I checked the signature panel on a document I saved and all the signatures applied says 'Signature validity is unknown', 'Signer's identity is unknown' etc. I checked out the attachment you sent and went to Preferences/Signatures and 'Verify Signatures When The Document Is Opened' is checked off. I'm lost, how to I made sure the signatures are valid?.

ls_rbls

Community Expert

When you are validating signatures You have right-click on the signature field, then click on "Show Signer's Certificate". This will bring up another dialogue box; from that dialogue box click on the "Trust" tab. Then on a button below in that tabbed window click on "Add to Trusted Certificates"; tick the check boxes that apply to whatever you want that signature to validate for. Then click OK button. This will bring you back to the previous dialogue box, where you are going to click on "Validate Signature" button again for the validation to take effect. You will notice in the right pane to the left of the screen that the validated signature will now show a green circle with white checkmark icon instead of a yellow triangle with white exclamation mark

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traceyc28668387Author

Inspiring

Thank you so much for the replies, it has been super helpful for me! I hope this isn't a stupid question, but is there a way to track if any changes were made before the last signature has been applied and locked? Is there something in the PDF that says if the second or third person prior to signing made some changes? Just curious

ls_rbls

Community Expert

Please see links below:

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margueritek

Inspiring

There is an option to "Lock" the document after a Digital Signature, and that should be used with the last signature. Note that flattening a signed document will invalidate all Digital Signatures. The Digital Signature itself, if the document is locked, is evidence that the document has not been tampered with -- the signature will be invalid if the document is changed.

abracadabraJRB

Inspiring

Hi.

All you want to know about refrying is in this document, wroten by Leonard R., aka the "PDF father": Refrying PDFs – the good, the bad and the ugly

==> https://abracadabrapdf.net/file/Refrying_PDF.pdf

Flatten means merging all form fields and comment into the layout, so they become just graphic objects, loosing their field/comment features.

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