I downloaded this PDF file from a website which is 350 KB in size with 20 pages. All pages are scanned images. I extracted the images using Adobe Acrobat Pro which are 1.32 MB in size collectively (view > tools > document processing > export all images). I converted them into a single PDF file (1.28 MB). How can I combine those images into a low-sized PDF file?

Do I need to reduce the size of scanned images with a software? So how can I do this to get the quality of that 350-KB PDF file?

In fact, I regularly scan some of my documents and convert them into PDF and I want to keep them as small as possible.

What I tried:

  • in Adobe Acrobat Pro: file > save as other > reduced size PDF
  • in Adobe Acrobat Pro: file > print > "print in gray-scale" check-box checked

update: Links removed due to copyright infringement!

  • Store on a compressed directory? Assumming windows OS. You can also winzip/pkzip each for compression. – mdpc Dec 28 '14 at 9:11
  • stored on a regular directory, not compressed. Yes, using Windows. Zipping and extracting each time? That's not practical. – living being Dec 28 '14 at 9:24
  • I mean set the directory to be compressed so that as you put things in it will be compressed automagically. For longer term storage and light use, I think that compression is quite practical on an individual file basis. – mdpc Dec 28 '14 at 9:25
  • The original pages look like a fax (not over 200 dpi black and white; could have been scanned that way), with a watermark on every page. That's why the PDF was so small, and how to re-create one of comparable size. – fixer1234 Dec 28 '14 at 9:37
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    @mdpc: I want to reduce the size of the file itself. – living being Dec 28 '14 at 9:41

What you did is useful as an exercise. Otherwise exporting images from a PDF like this and creating a new PDF out of those makes no sense.

The original document space usage is:

Description        Bytes      Percentage
Images             351,829    97.60 %
Content Streams    2,742      0.76 %
Document Overhead  5,916      1.64 %
Total              360,478    100 %

Your document's space usage is:

Description        Bytes      Percentage
Images             1,329,944  98.87 %
Bookmarks          21         0.00 %
Content Streams    1,675      0.12 %
Structure info     60         0.00 %
Document Overhead  13,389     1.00 %
Total              1,345,089  100 % 

The original document isn't created with Acro, but iText which explains the missing structure info.

Under Document Processing you have a separate tool "Optimize scanned PDF". I followed your workflow and run the optimizer on my newly created PDF, and the resulting file size is 328KB. However the quality is clearly worse than the original document.

This is to be expected, as I did everything with default settings. This means the image export was already done as jpg which anyway is larger than a PDF. I tested this just by extracting each page to a single PDF - for example the jpg image exported from page 1 is 22KB whereas exported as a PDF it's just 9KB. Optimizing the images further in the new document worsens the image quality even more. This is just unavoidable with bitmap image formats such as jpg.

The size usage above shows that Acrobat clearly exported the images with highest possible quality. This makes sense, as when you do this you want to get them out with minimal image data loss.

One option could be OCRing the file, which converts the images to text, and textual files are much lighter than image bloats. Acro Pro contains OCR tool, but I can't test this as I don't have Arabic available.

EDIT: Extended language pack only applies to Adobe Reader. After some research it seems that Acrobat does not support Arabic OCR. See this Adobe forum discussion.

Scanning into PDF and then optimizing is always a tradeoff between size and quality. You just need to test with different settings (both original scan and the optimization) to you find a satisfactory compromise.

Instructions for PDF optimization are in Acrobat Help. Help is available online for both Acrobat X and Acrobat XI

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  • they converted the images into PDF without OCR. So it is "possible" to do it with such a low size. What kind of solution we can use to achieve this? That's my question. Definitely there's a tradeoff between size and quality, but a document with this size and this quality is extant. – living being Dec 29 '14 at 4:09
  • Most likely yes. I don't really get the question - if you have a PDF which contains pictures with text, you can OCR it with Acrobat, but you will have to test yourself which settings give you an acceptable quality. There is no one-size-fits-all -solution. The only things I can think of that would decrease the file size is OCRing and optimizing. I added a couple of things to the original answer. – Peregrino69 Dec 29 '14 at 10:42
  • Of course there's not one standard size as you pointed out. I just meant that they achieved this size, but the size of mine is 300% more. That's a lot! + Using OCR is a pain in the neck. It cannot recognize all of the text correctly, especially for non-English languages. – living being Dec 29 '14 at 10:52
  • The original scanned images are simply smaller than what Acrobat exports. If you want to have smaller size exported images, you can choose lower quality, but that's just what it says - lower quality images. I updated the answer again with info about using Acrobat with non-English languages and non-western characters. If you're using Acrobat professionally I'd recommend getting training on it. Lynda (lynda.com) is the current provider of official Adobe training materials. – Peregrino69 Dec 29 '14 at 11:01
  • I used a professional software designed specifically for OCR called Readiris Pro and I did my best attempt to get a good result which has never been achieved (for this language) – living being Dec 29 '14 at 11:05

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