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I scanned a document and would like to crop out around half of the image.

I can crop using Preview or using Adobe Acrobat Pro. But neither program permanently crops the file. The file size never decreases.

  • I tried using "Remove Hidden Information" on Adobe Acrobat Pro which was able to permanently crop the file. After the process completed, I clicked Save which opened a new Save As prompt. So, I re-saved the document, but the file size grew tenfold. No idea why.

  • I tried exporting to Optimized PDF on Adobe Acrobat Pro and the PDF was still not permanently cropped.

  • I tried exporting to Reduced Size PDF on Adobe Acrobat Pro and the PDF was permanently cropped, but the image quality was decreased.

  • I tried exporting to PostScript on Adobe Acrobat Pro, and from that, creating a new PDF. The PDF was permanently cropped, but the image quality significantly decreased.

  • I tried creating a custom Preflight Fixup in Adobe Acrobat Pro, using "Set page geometry boxes". The resulting PDF was not permanently cropped.

Are there seriously no options to remove the cropped area without exporting the file as TIFF and importing the TIFF files to create a new PDF file or ->Print->Save As PDF? I don't want to do these because the image quality will decrease.

I'm on OS X but I also have a Windows machine I can use.

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3 Answers 3

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I do this all the time with Acrobat Pro and I used "set page geometry boxes". I just set it to crop all pages, then save the file. Did you actually save the file after the crop?

EDIT:

  1. Open the PDF with Acrobat Pro. We have version 10.1.12.
  2. Open the Tools sidebar by clicking Tools button at the top of the Acrobat window.
  3. Open the Print Production area of Tools.
  4. Click Set Page Boxes.
  5. Set your margins in the "Margin Controls" area.
  6. In the bottom right of the dialog, in the Page Range area, click the All radio button.
  7. Click the OK button.
  8. Save the PDF.
  9. Close Acrobat Pro.
  10. Check that your PDF file now has today's date and time to indicate it was changed.
  11. Reopen the PDF. It should stay cropped.

We need to retain high quality images because some of our customers use our PDFs to print their stuff (at another vendor).

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  • Before I answer your question, can you go into more detail about the method you are suggesting?
    – rubik's sphere
    May 31, 2016 at 18:46
  • I updated my answer above. What version of Acrobat Pro do you have?
    – Bulrush
    May 31, 2016 at 19:03
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    This method does not permanently delete the cropped area. The cropped area is simply hidden.
    – rubik's sphere
    May 31, 2016 at 19:45
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    I'm not sure what you mean. When we crop a PDF this way it prints like it was cropped. How do you know the cropped area was just hidden, can you reverse the process somehow? Do you want to crop the actual image not the whole PDF? If so you have to use an image program to do that, then recreate the PDF that contains the image.
    – Bulrush
    Jun 1, 2016 at 9:27
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    Yes, you can reverse the process. Complete your method and then re-crop a section of your PDF. When the "Set Page Boxes" window pops up, you can see in the right-hand preview of the crop the original PDF—it has not really been cropped. For more proof, using your method, crop out everything except a tiny area. The file size remains the same.
    – rubik's sphere
    Jun 1, 2016 at 11:48
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I don't want to do these because the image quality will decrease.

Cropping a picture (wheter in a PDF or not) requires to encode it again. Usually pictures in a PDF use a lossy compression, so you can't do that without losing quality. But most of the time you can achieve that with an almost unnoticeable quality loss.

The good news is that there is no need to spend a whopping amount of money for Adobe product. You can do that with GIMP:

  • Run GIMP
  • Open the PDF file
  • When asked for the pixel density (or resolution) insert the same that you used to scan the document (e.g. 300 DPI)
  • Use the cropping tool as you see fit (or any other editing tool for that matter)
  • Click on File → Overwrite [filename.pdf]

Note: this rasterizes any PDF. This is just fine for a scanned PDF because it is raster anyway, but it won't work very well for a PDF containing real text or vector graphics.

How to determine the pixel density of a scanned PDF

In case the document was scanned by someone else, you can find the resolution in this way:

  • Open the PDF document with Inkscape
  • Some PDFs show grouped elements, I suggest you ungroup all the things by:
    • Selecting everything with Ctrl+A
    • Pressing Shift+Ctrl+G a few times
  • Click on the picture

  • Look at the bottom bar to check its size (sorry for the picture in Italian):

    image size

  • Now look at the toolbar. Change the unit of measurement to inches and check the height:

    height in inches

  • Do the math:

    2814 / 9.379 = 300 DPI

The number might not be perfect, but you can decide to round it up to a "reasonable" value. The most common DPI values for scanned documents are 72, 90, 144, 150, 180, 200 and 300.

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  • This method is essentially what I mentioned in my question: "exporting the file as TIFF and importing the TIFF files to create a new PDF file." It permanently crops the image but it is lossy. Also, I don't know the DPI of the PDF and do not have access to the scanner used. Theoretically, deleting a cropped area of a PDF should not require compression.
    – rubik's sphere
    May 31, 2016 at 21:40
  • No. Only some image formats such as BMP and PNG are lossless. Theoretically based on what? We are talking about cropping a raster image and not a vector file. Did you actually try the method? You won't be able to tell the difference with your eye. BTW determining the resolution is very easy since you can export the original image and find out how many pixels it has.
    – Andrea Lazzarotto
    May 31, 2016 at 21:51
  • Yes, I actually tried the method. I used the default resolution, the file size was halved, and the quality significantly decreased. I don't know how to find the DPI of the original PDF.
    – rubik's sphere
    May 31, 2016 at 21:56
  • @user598115 The default resolution is usually 72 (very low quality). I added the steps to find out the correct value.
    – Andrea Lazzarotto
    Jun 1, 2016 at 12:29
  • OK. The DPI of my PDF is 300. I used the GIMP method using 300 DPI as the resolution instead of the default, 100 DPI. The PDF was permanently cropped. The image quality slightly worsened, but the quality was still high. However, the file size ballooned from 68.7 MB to 262.5 MB. The purpose of permanently cropping the PDF was to decrease the size of the PDF. So while your method technically works, it does not move me toward the underlying goal.
    – rubik's sphere
    Jun 1, 2016 at 13:59
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I believe you can do this in Preview, but you need to create a new document rather than cropping. To achieve this,

  1. Select the area you would like to "crop"
  2. Copy, by pressing command + C
  3. New from Clipboard, by pressing command + N

You should get the selected section without the rest of the image/document.

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  • 1
    This method does not permanently delete the cropped area. The cropped area is simply hidden.
    – rubik's sphere
    May 31, 2016 at 7:35
  • @user598115 - Right you are. The method I described only works for images opened in Preview - sorry!. You could export the PDF file to an PNG (image quality lossless, but you lose scalability) first using Preview, but I think you don't want that. Alternatively, you could make an Automator Workflow, which would crop and create a pdf again, but you would have to have a pre-defined crop area.
    – lindon fox
    May 31, 2016 at 9:45

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