Transparency in PDF files refers to objects on a page (images or text) that are transparent.
Full transparency refers to making an object, or part of an object, fully invisible. Partial transparency is more complex. A certain proportion of both a foreground object and anything in the background needs to be blended together.
The PDF standard has supported transparency since PDF 1.4 and Acrobat 5. It is continuously improved by Adobe. When PDF documents with transparencies are printed on PostScript printers, the printing application must flatten the transparencies first, because PostScript does not support transparency.
Transparency can be used for many reasons:
- To show parts of objects that are normally hidden.
- To lighten images so that the text on top remains readable.
- To create a tint of a specific color or to mix colors.
- To make underlying image objects show through. Transparency enables features such as drop shadows, feathering, soft edges, blurs, and glows, as well as partial transparency of overlapping objects. Adding a drop shadow to text or images is one of the most common uses of transparency.
How is transparency added to a PDF?
Actions that add transparency to a layout:
- Feathering objects.
- Adding drop shadows to objects.
- Placing native files that contain transparency from Adobe Illustrator, InDesign, and Photoshop.
- Dragging and dropping (or copying and pasting) transparent objects from applications like Adobe Illustrator to Adobe InDesign.
Today, every mainstream file format and graphics application supports transparency.
