There are basically four kinds of PDF export targets. It’s important that you consider the hints below before you start creating your documents.
Press Optimized: All bitmap images brought into to Scribus as placed images should have a minimum resolution of 200 dpi and preferably 300 dpi or more for photos or TIFFs. For line art or vector graphics converted to a bitmap image, an even higher resolution may be necessary for best results. Most vector files can be imported directly as native Scribus objects, which is recommended if possible. Output target in the PDF Export dialog: “Printer,” unless you export to PDF/X-3.
Print Optimized: This would mean targeting the PDF for printing on an office laser-jet or ink-jet. Recommended settings: Down-sample all images to 300 dpi or less, embed fonts and keep your page margins with enough tolerance for margin limits on desktop and common office printers (approx. 6/10th of an inch or 1.5 cm). Do not choose “Printer” as an output target, but use “Screen/Web” instead, as ink-jet and laser-jet printers expect RGB input.
Web download, screen reading, interactive forms: See the section on Screen/Web export.
Presentation Effects: See the section on PDF presentations.