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Hidden data in acroform

New Here ,
Aug 20, 2021 Aug 20, 2021

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Hi everyone

 

I have a very strange problem with a PDF form created with Acrobat. It's a simple acroform without any JavaScript. The form contains just a couple of text fields to enter a name, phone number, address, etc. I created the form, typed in some test data, resetted the form and sent it to people to fill it out. The form was obviously empty. But still, one of the recipients was able to see the mentioned test data I typed in before resetting the form!

 

I checked the internal PDF structure with Preflight and was not able to find the test data. But when I open the PDF with a simple text editor I actually find some of the test data I entered, although I resetted the form:

 

2021-08-20_14h43_53.png

 

This raises several important questions:

 

  1. How is it possible that there is still “hidden data” in the form even though I resetted the form?
  2. Why/under what circumstances is an end user able to see this data?
  3. Most important: How do I make sure, that my forms do not contain this kind of hidden data?

 

Thx a lot for help!

 

Regards

 

Thorsten

 

 

TOPICS
Create PDFs, General troubleshooting, PDF forms

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correct answers 1 Correct answer

LEGEND , Aug 21, 2021 Aug 21, 2021
Removing and re-adding the fields is NOT going to solve this problem. The "orphaned" info will remain if the signature is in place. You may be able to copy/paste fields into a new document. I always advise to treat signing, reader enabling and setting security as irreversible, and to carefully backup first. I think Reader enabling is obsolete for most people today.

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Adobe Community Professional ,
Aug 20, 2021 Aug 20, 2021

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This is just a guess, but try saving as an optimized PDF (File> Save as other> Optimized PDF). One of the settings may remove the unwanted info. If it works, you can create an Acrobat Action to easily apply it to a PDF or folder of PDFs.

 

optimize for content.png

 

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LEGEND ,
Aug 20, 2021 Aug 20, 2021

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If you use SAVE all your changes are added only to the end of the file. Replaced info isn't accessible, but it is there in the file. If you don't want this, end your work with SAVE AS.

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New Here ,
Aug 20, 2021 Aug 20, 2021

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Thx a lot for your answers! But that is not enough. Unfortunately, the data is still there. I tried both ("Save as" and "Save optimized"). Still I am able to find the unwanted, hidden data...

 

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Adobe Community Professional ,
Aug 20, 2021 Aug 20, 2021

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Can you share the form?

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New Here ,
Aug 20, 2021 Aug 20, 2021

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LEGEND ,
Aug 20, 2021 Aug 20, 2021

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My guess: this file is signed, perhaps Reader enabled. A signed file does NOT reclaim space or remove deleted items when you save it, because that would destroy the signature. So your lost form field info is stuck there forever.

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New Here ,
Aug 20, 2021 Aug 20, 2021

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Yes, you are right. Reader Extensions are enabled. BUT if you "Save as optimized PDF" the signature should be removed:

 

2021-08-20_18h36_23.png

 

But unfortunately, the unwanted information is still there. Even if I reset the form one more time...

 

https://drive.google.com/file/d/170XPvxNGC-TbiL95ZpGJs1YwFOLESgkI/view?usp=sharing

 

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LEGEND ,
Aug 20, 2021 Aug 20, 2021

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Yes, it should. But in my tests, despite the message, the file was still signed after the optimization was complete! This might be a bug. 

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New Here ,
Aug 20, 2021 Aug 20, 2021

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Is there a reliable way to remove the signature?

 

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New Here ,
Aug 21, 2021 Aug 21, 2021

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There seems to be no way to remove this hidden information. Even Tools -> Protection -> Remove hidden information does not work. I still don't know why. But enabling extended reader functionality is my best guess....

 

Is there other 3rd party software that is able to remove this hidden data?

 

Thx a lot and have a nice weekend! 🙂

 

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LEGEND ,
Aug 21, 2021 Aug 21, 2021

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I suggest you go back to the last backup before adding reader extensions, and proceed from there. 

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New Here ,
Aug 21, 2021 Aug 21, 2021

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I started to remove all form fields and add them again one by one.... 

 

Extended Reader functionality seems to be somehow dangerous, since it is not reversible anymore. Is Extended Reader functionality still necessary today to save a filled in form?

 

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LEGEND ,
Aug 21, 2021 Aug 21, 2021

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Removing and re-adding the fields is NOT going to solve this problem. The "orphaned" info will remain if the signature is in place. You may be able to copy/paste fields into a new document.

 

I always advise to treat signing, reader enabling and setting security as irreversible, and to carefully backup first. I think Reader enabling is obsolete for most people today.

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New Here ,
Aug 21, 2021 Aug 21, 2021

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Thanks to all the great people here for helping me understand the issue!!

 

The best advice is actually this one from "Test Screen Name":

 

"I always advise to treat signing, reader enabling and setting security as irreversible, and to carefully backup first. I think Reader enabling is obsolete for most people today."

 

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