Transparency is such an integral part of Illustrator that it’s possible to add transparency to your artwork without realizing it. You can add transparency to artwork by doing any of the following:
Lowering the opacity of objects so that underlying artwork becomes visible.
Using opacity masks to create variations in transparency.
Using a blending mode to change how colors interact among overlapping objects.
Applying gradients and meshes that include transparency.
Applying effects or graphic styles that include transparency, such as drop shadows.
Importing Adobe Photoshop files that include transparency.
For a video on working with transparency, see www.adobe.com/go/vid0054. For more information on working with transparency across Adobe Creative Suite, see www.adobe.com/go/learn_ai_transparency_pdf.