Following Safe size for printing image from browser, I saved my Illustrator file with vector drawings as a PDF. It weighs three times more than the PNG export of the same file at 300 ppi, 4.2 MB versus 1.5 MB. The Illustrator file, saved without the PDF compatible file, is 2.7 MB. Here is the design, saved at 72 ppi:
On another design without a drop shadow, the PDF is 538 KB and the PNG is 228 KB.
Why is the PDF file much larger for purely vector art?
Update: Here are the main settings when saving as PDF (general and compression, and I can add the others if relevant):
Answer
Since you haven’t shown your PDF export settings, I can only make some guesses.
If you have the “Preserve Illustrator editing capabilities” option checked when exporting the PDF, that could explain a larger than expected file size. Basically, that setting saves both the AI file data and the PDF data in the one file. Try disabling it. Obviously, make sure that you’ve saved your AI file first, since the PDF will no longer be properly editable in Illustrator.
Effects such as drop shadows will be rasterized when exporting to PDF. If your PDF settings are set up for high quality printing, this means you could have one or more large raster images contained within the PDF. PDFs can contain both raster and vector images.
Also there’s no guarantee that a pure vector image will be close to a PNG’s file size. Vector file sizes depend on how many paths, anchors and individual objects there are in the design (i.e. the amount of data), and the file size of a PNG will depend on how many pixels are in it, and the colour mode (i.e. indexed versus RGB, or RGBa). Vector and raster file sizes are not really comparable.
Attribution
Source : Link , Question Author : miguelmorin , Answer Author : Billy Kerr