Why does Remove Hidden Information and Sanitize Document cause file size to increase 2-10x?

[Guest]

Using book-scanning services, I have books scanned into pdf files as 300dpi images. Using Acrobat DC Pro, I run the Recognize Text tool within the Enhance Scans category (which actually decreases the file size). I then, within the Redact category, try to Remove Hidden Information or Sanitize Document, and the file size explodes upward. As a representative example, this is what happens:

Step 0: Book as received from scanning service: 19MB

Step 1: Book after running text recognition: 13MB

Step 2: Book after running Remove Hidden Information: 53MB

or: Step 2: Book after running Sanitize Document: 22MB

Incredibly, not only does the file size increase dramatically when removing information/sanitizing document, but, to put salt on the wounds, the image quality also decreases noticeably! This always happens, with no exception.

1) Why does this happen? Intuitively, I would think removing hidden information would actually reduce file size, especially if the image quality deteriorates.

2) Is there any solution to this?

3) Assuming there is no good built-in Acrobat solution, is there any third-party software alternative to sanitize pdf documents that doesn't cause file size to explode up?

[Adorobat]

Hi sammyb81891914,

This is a known issue and we are working on it. As a workaround, you might try optimizing the pdf file to make it PDF version 1.7 and compatible with Acrobat 10.0 and later.

Thank You for your patience.

-Shivam

[HenryChang2]

Hi, I optimized my file to make my PDF compatible with Acrobat 10.0 and later, but "Remove Hidden Information" or "Sanitize Document" still make the file size explode.

Is there any detailed steps that we can follow? Thanks!

[jonathans50599891]

Any updates on this?

Still an issue on Adobe Acrobat Pro 2017 Mac  (17.11.30105)

[Dhimant0D44]

its 2021 but no update. same problem exists..

[default6o5i8k43u3z4]

Agreed. First time really using Adobe Acrobat Pro DC and i'm running into this exact issue. Quality of the image diminishes tenfold. 

[scottf67571169]

Shivam,

Please refer to the following thread: forums.adobe.com/thread/1396892

This problem has been known for 4+ years! Please don't tell me that you are working on it if you're not actually working on it. Instead of copping out, how about you actually do the work?

Or please just tell me the truth: Adobe doesn't care enough to fix it so deal with larger file sizes or don't use the tool.

[William5D9B]

Known issue since January 2017, probably earlier. Nearing 2021, still not fixed, like nearly every other issue. Just experienced this same problem that I've been experiencing for years.

[Allen Cobb]

I just redacted and sanitized a couple of PDFs, and the file size stayed roughly the same, but the resolution of the display dropped drastically, to a fuzzy unusable lack of sharpness. So the whole redaction tool still isn't usable.

Or is there some way to preserve the quality of a PDF after it's been redacted and/or sanitized?

[joani55343265]

My file looks awful and the size is huge. I see this has been an issue for many years, when can we expect to see a fix to this issue?

[Kevin5E1D]

This issue is still present.  We get file sizes that are ~3x the original, when we run Sanitize.

If we Optimize, we get to remove what we select and the file size stays roughly the same size or shrinks a bit.

Please fix this issue.

[pj0D4C]

Apart from selecting any changes you want to make individually;

once ready to save

Try

Save As - Adobe pdf Optimised  select Settings

within settings select Clean Up    change option to  Leave Compression Unchanged

( I also use compatibility as Adobe 6.0 onwards )

That seems to work for me

[percjake]

2024 and the problem still exists. I'm using the sanitize function to remove hidden text artifacts because they slow down viewing of pdfs of music. Opening in photoshop shows that this inexplicably resamples bitmap (black and white) images to a lower resolution in RGB (full color), which both severely diminishes quality and increases file size. Why are we paying out the wazoo for a program whose developers leave bugs like this in place for EIGHT YEARS? 

[ruben5C2D]

this is so pathetic this is still happening.

[Link648099]

This problem is still happening.

Adobe developers are next to useless.

[Mandy37139483g2wy]

This helped me for my purposes. Change the preference to retain overlapping content, redact and don't sanitize.  Then, sanitize it.  My orignial doc was 8.5 MB. When I redacted & sanitized together, it took my file size to 20 MB.  When I redacted, saved, and then sanitized all, it took my file size to 12 MB.  When I redacted, saved, then sanitized retaining OOs it took me to 29 MB.  When I redacted, saved, sanitized retaining OOs, saved, then went back in and sanitized the OOs it took me to 17 MB.  
How to prevent PDF file size increase after redaction (adobe.com)

[marco-b]

The weirdest part about Adobe not fixing it is that using an action to remove hidden information actually greatly reduces the size, using Sanitize to do the same bloats the file by around 20%