What is transparency?
Transparency in PDF files refers to objects on a page, such as images or text, which are transparent or allow other images or text layered underneath them to show through. These images or text are partially or fully see-through. Transparencies can look great on screen and create a lot of unique effects, but that does not always translate well to viable printing.
Transparency uses in PDF files
transparency or partial opacity
lightening parts of image so text on top remains readable
making objects fade into another object
blend to create a tint of a certain color
drop shadows
glows
feathering an image
placing or importing native files which contain transparency from Adobe Illustrator, InDesign or Photoshop
copying & pasting transparent objects from applications like Adobe Illustrator to Adobe InDesign
Print Ready PDF files
Ideally, print ready PDF files should contain no transparency to ensure that they will print exactly as they look. View the flattened PDF file with overprint preview turned on in Acrobat before submitting.