As shown in the screenshot the "Adjust Size" is disabled and grayed-out for the given PDF:

Preview > Tools > Adjust Size...

So how do we reduce the size of a pdf in preview (or even skim?)

  • Try making a selection on the PDF, then try ⌘K to crop? – perhapsmaybeharry Feb 16 '16 at 23:17
  • @perhapsmaybeharry cropping selects a portion of the pdf but does not resize the selection. The intent here is to retain the (entire) selection and reduce its resolution – StephenBoesch Feb 16 '16 at 23:33
  • Ah, I understand. You want to scale the image. Like Dictionarics Anonymous indicated, Preview only does this on images and not PDFs. – perhapsmaybeharry Feb 17 '16 at 2:32
  • @javadba did you ever solve your problem? – Natsfan Dec 18 '17 at 22:48

I did not find out how to do this in preview or skim: so a "real" answer would still be awarded.

However there is a workaround when printing: the print dialog for my HP laserjet has a "Scale" that can be applied. This took care of my immediate need.

enter image description here

  • This was the most useful for me too. – PatrickT Jun 27 '17 at 16:42

The Adjust Size / Colour feature in Preview doesn't work for PDF files, only for bitmap image files. Usually you don't want to change the format of a PDF document, anyway.

However, if you have a PDF file that contains only embedded bitmap images, and you want a downsized version of that image, it's possible to use the Preview's export feature: File > Export. The export dialog will ask for a pixel density (in ppi) to use for the export, as it is assumed that you are converting vector graphics/text to bitmap graphics…

Another possibility is to use the marquee/selection tool to select an area or the whole page and press Cmd-C, then create a new Preview document from the selected area by pressing Cmd-N, and save the new document in a bitmap format.

I can't say what it does to the exported image if you put in a ppi value different from the actual ppi value of the embedded image. There are commercially sold third-party tools that extract bitmap images from PDFs without resampling them, e.g. Acrobat Pro/DC and others. A smaller and free tool is downloadable via SourceForge: https://sourceforge.net/projects/pdf-images/

  • Thanks - those are probably the only options. They are not adequate for my particular circumstances. However I am going to upvote (though not accept) anyways - since your points are valid and probably helpful to others reading this question. – StephenBoesch Feb 17 '16 at 2:50

The following approach worked for me in Mac OS X 10.13 (High Sierra):

  1. Open PDF to shrink in Preview
  2. Select File -> Export
  3. Leave format as "PDF". In "Quartz Filter" select: "Reduce File Size"
  4. In "Export as", I changed the file-name e.g. added "_small"; so I don't overwrite the original.
  5. Press on "Save"

You don't have any control on scaling parameters, but results were good enough for what I needed.

  • 1
    The question is how to reduce the physical dimensions of a PDF, not how to reduce the file size. File Size reduction has been dealt with in other questions. – benwiggy Jul 11 '19 at 6:42

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