Knowledgebase

Summary

In the PDF specification Layers are handled a differently than in most other software, such as graphics applications (Coreldraw, GIMP, Photoshop, etc), and as a consequence have some limitations in how they are used. This article is intended to help explain what those differences are and how they affect the way "Layers" are handled our products.

What exactly is a "Layer"?

In Graphics applications (Not our PDF-XChange Editor, or any competing PDF editing software), Layers will often refer to a section of the content in a file that is distinctly on top of whatever layers are "behind" it, and behind the layers that are "in front" of it. In this scenario there exists a "Z axis" to determine the order of content, and any layer above the bottom layer would generally have a level of transparency so that the layers behind remain visible.  When you "bring forward" or "Send backward" content [image?] you are manipulating the "Z order" of the object(s).

In the PDF specifications, "Layer" is a term that was used by the Graphics industry and Adobe in particular used it in the context of PDF files.  It is actually a somewhat misleading description of what is happening, yet is commonly accepted as the "standard" name for this function. More appropriate terms for "layers" in the PDF format may be "Optional content groups", or "Visibility groups". There is no "Z axis" as there is no true order for layers in this format. Layers are instead intended to toggle the visibility of content, such as to quickly show or hide annotations, or to have a single document that displays for example a specific language, depending on the readers system locale.

How should I be using "Layers" in my documents then?

In essence, They are designed for "smart" documents which change which content is visible based on specific criteria. There are a few different use-case scenarios for Layers in a PDF document.  Note that when creating a layer, it is possible to configure some options that cannot be changed after creation, so it is always a good idea to look into these functions before beginning.

As an example, you can setup a layer which detects the system language, and will show a "French" layer, while hiding the "English" layer, if the users PC is French based. This allows you to have a single Multi-lingual document to share with people worldwide. Similarly, you could tie a graphic or text block/explanation to some radio buttons on the page, so that when you switch between "table" and "pie chart" radio buttons, you get a different graphic beside them, without the confusion of them overlapping in normal day to day use.

Here are some other common uses: