Comment 1 for bug 171774

Originator: YES

OK I think I have found the answer by myself on
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/File-Export.html#File-Export-Other
:

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 .pdf (PDF). Text is automatically converted to paths. The following
features are unsupported: Gradients on stroke, clipping, masking, patterns.
(Note: Evince, a popular Linux Postscript and PDF viewer does not show
gradients with transparency, use Acroread instead.)

Saving PDF via a Postscript file removed in v0.45.

Expect great improvements in PDF export in the next Inkscape release! A
Cairo based exporter is almost ready.

Export to PDF produces uncompressed PDF files (which is legal according to
the standard). Some operating systems and display software may complain.
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I hope in future version we'll have the possibility to choose the
compression level for the pdf output file :)