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I have a nice high resolution PNG. (Download from Dropbox) When I paste this into a new Word document, it looks good. I can't zoom in more than 500% but at that zoom level all lines are smooth, as expected.

Now I click File > Save as and select PDF from the Dropdown. From Tool > Compress Images (right next to the save button) I select "use document resolution". Then, I hit save.

Expected: The image in the PDF (viewed in Adobe Reader) should have a similar quality as the PNG.

Reality: The Image is much worse than the PNG. Maybe downsampled to 96ppi.

Notes:

  • When I am in the save dialog and I go again to Tools > Compress Images, the selected option is reverted to "E-Mail (96 dpi)"
  • I tried the same thing on a diffewrent computer with Word 2013, but no luck.
  • I tried a different PDF viewer - same image quality
  • I tried to encode normal 96 ppi within the PNG and resize the image in word.
  • The option "do not compress images in file" is enabled. (This option)
  • This is obviously a reduced problem, so don't suggest GIMP. My real file has some text in it. Until now I am just reluctant of redoing it all in LaTeX.
  • The problem gets worse, when the image is further reduced within word. This points to a resampling going on when the pdf is created.

Additional thing I have tried:

  • When I use "Printing (220ppi)" instead of "document resolution" there is no discernible difference. (After all I thought that "document resolution" means that no resampling takes place and the full resolution is used.)
  • Exporting to XPS format has the same characteristics.

Question: How can I preserve the image quality when exporting to PDF?

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Compliments to this very accurate and neatly detailed question! I wished every question would be like this. What kind of Office are you running? I gave it a shot with Office 2007, Microsoft's PDF plugin, a high-res png and the pdf came out alright –  Zerobinary99 Sep 15 '13 at 14:51
    
Thanks :-) I use Word 2010, but have the same issue with Word 2013 on my laptop. –  DasKrümelmonster Sep 15 '13 at 14:53
    
FWIW I don't know of a way other than using a 3rd-party PDF maker with the relevant higher-res settings. –  bibadia Sep 15 '13 at 15:32
    
I would use Ginmp to open the PNG files and then export each to PDF. Check the result for quality and see if it's up to your standard. :) –  Darius Apr 17 at 18:14
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2 Answers

Word scales the image automatically depending on the paper size, so you need to increase it to increase the PDF's resolution.

  • The PNG you want to turn into pdf has a resolution of 1600x1600, so use a paper size that reflects this aspect ratio. Set your paper size to 55.87cm x 55.87cm (biggest Word 2007 supports)

  • Import the PNG and stretch it out to the maximum size the page supports.

  • Export it to PDF and enjoy your high res pdf :)

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The real document should be 85mm by 55mm, and the image is 10mm by 10mm. Changing that is not really a solution imho. The printer supports something like 600dpi, so 96dpi will definitely look blurry. –  DasKrümelmonster Sep 15 '13 at 15:04
    
You can print the PDF in any size you want. Downscaling is preserving the quality. Try my solution and adapt it to a multiple of your expected resolution like 51cm x 33cm. Printing it to a smaller sheet with the same aspect ratio will preserve the image's quality. You could also get a proper pdf-plugin for Word that offers more options than the rudimentary built-in pdf support. –  Zerobinary99 Sep 15 '13 at 15:15
    
I am trying. Ans while this solves the problem for a single image, it is not easy for an existing dicument. Scaling all the font sizes as well as the coordinates of tables, textboxes and images by 6 is a PITA. I consider this more of a workaround than a solution - after all, resampling still takes place. –  DasKrümelmonster Sep 15 '13 at 15:45
    
You wrote in your description that you "use document resolution" as a setting for the file. Using the original sheet measurements of 85mm x 55mm will thusly result in pixelation as the document resolution is just too low. I agree that adjusting the font sizes this way is a pain, but other than using third party add ons there's probably little you can do. You could try installing the pdf-update for Office 2007 since it doesn't have the options you described and may be allows for what you want. Other than that I can only recommend using Nitro PDF or something similar. –  Zerobinary99 Sep 15 '13 at 15:50
    
Another solution would be edit your pdf with an editor and replace the low-res picture with a high-res version. There are free editors available. There's even one that allows you to edit pdf-files online in your browser if you don't mind the lack of data security. –  Zerobinary99 Sep 15 '13 at 15:51
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Any easier solution might be to forego the in-built pdf conversion and use a pdf printer (I use pdfcreator from sourceforge.) You'll likely find finer grained control (including DPI settings of the printout - start w/ 600x600 but it supports up to 2400x2400 iirc).

This may be an easier solution as it won't force you to reformat existing docs. It's also free.

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