What if they made a feature no one could use?
When Adobe released Acrobat 6 Standard ($299; www.adobe.com) last May, the program could display layers in PDF files for the first time. But there were no Mac programs that could produce layered PDF files -- only Microsoft's Visio and Autodesk's AutoCAD could, on the Windows side. Then came Adobe Illustrator CS ($499) and InDesign CS ($699).
I'll explain how to create layered PDF files in these programs, and how to put the new capability to work in projects such as a bilingual brochure and a multilevel map. Note that these techniques are for PDF files destined for on-screen environments -- such as DVDs, kiosks, and e-books -- not those that will be used in print projects.
Go Straight to the Source
You can't generate layers in Acrobat. Instead, you build them in a program that supports layers; then you export them as part of the PDF-creation process. Not all programs that have layers can export layered PDFs; for example, Photoshop CS can't. Also, Acrobat Distiller and other PDF-creation programs don't create layered PDFs; you can't produce layered PDFs from, for instance, QuarkXPress or Macromedia FreeHand.
A Bilingual Brochure
Say you're using InDesign to construct two versions of a digitally distributed travel brochure: a French one and an English one. Without layered PDFs, you'd have to force some viewers to scroll past a page in one language to get to the other language. Now you can output a layered PDF that includes language buttons; your potential traveler simply clicks on the appropriate button to choose a language.
Create Layers and Buttons in InDesign On the second page of your InDesign document, use the Layers palette to place the English text in one layer and the French text in another. On the opening page, use the Button tool to create buttons labeled "English" and "French." Select each button in turn and choose Object: Interactive: Button Options. Click on the Behaviors tab and set the behavior to Go To Next Page. Click on Add and then on OK.
Export to a Layered PDF To export the layers correctly, go to File: Export and choose Adobe PDF from the Format menu. Click on the Save button and set the Acrobat options in the resulting window. Choose Acrobat 6 (PDF 1.5) from the Compatibility drop-down menu, and select the Create Acrobat Layers option and the Interactive Elements option.
When you open the PDF in Acrobat 6 or Adobe Reader (a free download at www.adobe.com/products/ acrobat/readstep2.html), the layers will be listed in the Acrobat Layers pane. (Layered PDF files also have an adorable little layer-cake icon in the lower left corner of the document window.) If you open a layered PDF in previous versions of Acrobat, Reader, or Preview, all the layers display and you can't change their visibility.
Set Layer Visibility You can't apply layer-visibility actions to buttons in InDesign. Instead, you'll have to turn to Acrobat's button controls. Activate them by going to Tools: Advanced Editing: Show Advance Editing Toolbar and clicking on the Button tool.
Open your brochure PDF file, click on the Layers tab, and turn the English layer on and the French layer off. Then go to the first page of the brochure. Double-click on the English button to open Button Properties. Under the Actions tab, use the Select Action menu to add the Set Layer Visibility action to the button. Click on Close and repeat these steps for the French button, turning the English layer off and the French layer on. Now when someone clicks on one of the buttons, Acrobat will display the page with the appropriate language.
A Multilevel Map
Layered PDFs are also a blessing for projects with many complex details. Consider a city map distributed on the Web or on a CD. When you zoom out to see the entire city, the view reduces street names and other small details to meaningless clutter. It would be better to see only larger details, such as highways. But when you zoom in on the map, small details are crucial.
Create Layers in Illustrator Illustrator's Layers palette lets you place the thin lines indicating local streets on one layer, and the thicker lines for major highways on another (see "Map Magnifications"). Beware -- only the top-level layers translate into PDF layers, so don't use sublayers.
Save as a PDF To create the PDF from Illustrator, choose File: Save As and select Adobe PDF from the Format menu. When you click on the Save button, you can set the Acrobat options. As in InDesign, choose the Acrobat 6 (PDF 1.5) compatibility option. Then choose the Create Acrobat Layers From Top-Level Layers option.
Zoom In with Bookmarks Buttons aren't convenient for displaying map layers, because as you zoom in to a new area, you lose sight of the buttons that control the zoom. Change the layer display using bookmarks, which are always visible in Acrobat's Bookmarks pane.
In Acrobat, use the Layers panel to make the zoomed-out map visible and the other layers invisible. Set the zoom level with the magnification control. Click on the Bookmarks pane and the Create New Bookmark icon. Select the new bookmark, name it, and choose Properties from the Options menu.
Under the Actions tab, go to the Select Action menu and add the Set Layer Visibility action to the bookmark. This creates a bookmark that sets the zoom level and changes the layer visibility. Repeat these steps for each detail level of your map.
Don't Stop Here
Layered PDFs have a place in many other projects. In a catalog, try putting a product's different colors and styles on separate layers. Or employ layers for a class workbook, with test questions on a student layer and answers on a teacher layer. There's no limit to how you can use layered PDFs.