Created attachment 122938 [details] open letter - just an example! When I save the document attached as PDF with the Linux (I am using Lubuntu 14.04.4) version of LibreOffice (Version: 5.1.0.3), then the file size of the PDF is around 251 kB. When I save the document attached as PDF with the Windows version of LibreOffice (Version: 5.0.4.2 x64), then the file size of the PDF is around 161 kB. Why is that?
It might have something to do with the image compression settings. Check that both have the same quality % for JPEG compression in the PDF export dialog. Also, the Linux version might use a different compression library. Let us know, how it goes. I think this does not really qualify as a bug report :) These types of questions are better to first throw on http://ask.libreoffice.org/
Thank you for that hint! Indeed the Windows and the Linux version of LibreOffice have different default settings for PDF export. Default settings for images in Linux: "lossless compression" (or something like that, in German it is "Verlustfreie Komprimierung") Default settings for images in Windows: "JPEG compression" and "reduce image resolution" (to 90%). When I set the same settings for images in Linux, the resulting file size is nearly the same as with the Windows version of LibreOffice.