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I am looking for a tool that will shrink the size of a PDF file at the expense of quality. The software must:

  • Run on Microsoft Windows 8
  • Be free software (i.e. libre software or free as in freedom - not free as in free beer)

It would be nice if it has a GUI.

I found http://www.alfredklomp.com/programming/shrinkpdf/ which has 2 flaws: It is for a UNIX system and it has no GUI.

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    I know you are looking for a desktop tool, but for the sake of sharing info, this online tool is working very good at shrinking the size of PDFs -> smallpdf.com/compress-pdf – Mohammed Joraid Aug 12 '15 at 16:45
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    The problem with that is that I have no control over who listens in on the conversation: I cannot use it for confidential PDFs. This is also the reason I need the software to be free - I need to be able to check for backdoors. – Ole Tange Aug 12 '15 at 18:10
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For simple compression, use QPDF: it's also available in Windows, I believe there are graphical frontends too. qpdf --linearize input.pdf output.pdf

If you want a smart compression without too much thinking and the documents are for your own usage, forget PDF and convert them to DjVu, which is much more compressed especially on documents with many pages. There are many options but pdf2djvu is the easiest: pdf2djvu -o output.djvu input.pdf. Some GUIs available: pdf2djvugui2 (GPL), PdfToDjvuGUI (freeware).

If that's not enough, and assuming your issues are with embedded images, you don't have many options: you need to extract the images and resave them with a different quality, format or compression. It's very easy in convert to alter JPEG quality and compression for PDF, but such rasterised operations can be quite terrible.

  • The typical use case is compressing scanned pages harder, and smallpdf.com/compress-pdf works really well for that. I was not able to get QPDF to do the same. – Ole Tange Oct 5 '15 at 20:43
  • Ok, "Reduce your scanned PDF files to 144dpi" is what it does. Depending on what sort of images the PDFs contain and how big they are, convert -resample 144 in.pdf out.pdf should do the trick although it's very simplistic. – Nemo Oct 5 '15 at 20:56
  • Note that djvu is based on raster images, and PDF is a vector-based format in general, unless you have PDF that are 100% scanned images, there is nothing to be gained from this kind of conversion. On top of that, djvu uses an algorithm called jbig2 which is also available for PDF files, so by converting from PDF to djvu you may even run the risk of losing image quality without any reduction at all in file size. – yms Dec 7 '15 at 15:43
  • @yms the compression doesn't tell the whole story; DjVu tools are more readily available to perform the split in layers etc. that makes the DjVu files so efficient. Last time I looked, only pdfbeads did something similar and dependencies made install hard. P.s.: I assumed raster images because otherwise the question's "at the expense of quality" wouldn't make much sense for normal vector documents. – Nemo Dec 7 '15 at 22:53

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