Converting colors in PDFs

Hypothetical yet common scenario: you’ve received a PDF from a client that contains graphics to be placed into your InDesign layout. Unfortunately the graphics are in a colorspace not allowed by your job specs. What do you do?

Often, if the PDF was exported from Word or some other MS Office application, it will include RGB colors. While many modern print workflows will convert RGB to CYMK on the fly, If your document is printed using black ink only, or perhaps black and a spot color, then this is certainly going to be a problem, as that process color content will generate unwanted CMY plates. In this article I’ll explain how to use Acrobat Pro to convert all colors in a document to a specified colorspace, as well as how to use Illustrator to convert process colors to spots. Both of these methods can remove unwanted colorspaces from PDF content without rasterizing or otherwise reducing quality.

Convert Colors in Acrobat Pro

Acrobat Pro can easily convert all color in a document to a specified CMYK, RGB, or grayscale color profile. I always use this method to quickly correct PDFs that must be placed into books that are printed with black ink only. To convert colors in Acrobat Pro version 9 or 10:

  1. Open the document in Acrobat Pro.
  2. Go to Advanced menu: Print Production: Convert Colors
  3. Make sure that the “Convert Command:” is set to “Convert to Profile” (this is the default)
  4. Set “Conversion Profile” to an appropriate value. For grayscale, choose “Dot Gain 20%.”
  5. Select page range to convert at the bottom of the dialog. I usually just convert all pages (the default), especially if I’m placing multiple pages of the PDF into my InDesign layout.
  6. Click OK and then use Save As to save with a different name (just in case you need that original color version later).

If you do this a lot, I’d recommend showing the Print Production Toolbar in Acrobat Pro so that you don’t have to use the menu every time. To do this, go to the Advanced menu: Print Production: and choose “Show Print Production Toolbar.” The toolbar has other great tools on it that you might find useful as well.

Converting Colors in Illustrator

First of all, it’s important to understand that Illustrator can edit PDFs, often with more control than Acrobat. In fact, AI files are really PDFs! Of course, Illustrator generally only allows you to edit one page of a PDF at a time, so I typically only use Illustrator to edit PDFs when I need to make changes to a file that cannot be made in Acrobat.

If I need to have more control over the color than simply forcing it all into one colorspace then I turn to Illustrator. For example, I lay out a quarterly publication that is printed 2-color. It contains charts that are exported from Excel. I need to convert the colors used in the chart to tints of either black or my spot color.

The method I use to do this in Illustrator CS5 is as follows (older versions should be similar):

  1. Open the PDF in Illustrator. If it’s a multipage PDF, Illustrator will prompt you to select the appropriate page.
  2. Change the document color mode to CMYK (File: Document Color Mode).
  3. Remove any unused swatches from your swatches panel. Find the Swatches Panel in the Window menu if it isn’t on your screen, then click the Swatches Panel’s menu button and choose “Select all Unused,” then click the trash icon at the bottom of the Swatches panel to delete them.
  4. Add used colors to your swatches (Swatches Panel Menu: “Add Used Colors”). When swatches are added this way they are global, meaning that changes to the swatch will affect any objects using that swatch, and this is exactly what we want.
  5. Deselect everything while editing color swatches to avoid accidentally applying color to objects.
  6. Change the new “black” swatch to true 100K. One of the new color swatches will probably look black, but its color values will display a mix of CMYK because it was converted from a RGB color. Double-click it to edit, make sure “global” checkbox is enabled, and move CMY sliders to 0% and K slider to 100%.
  7. Change your color swatch to spot color matching your InDesign color. You’ll have at least one other new color swatch that matches one of the colors used in the charts. Double-click the swatch to edit it, change the Color Type to “Spot Color.” For selecting what color to use, I’ve found it easiest to enter the name of the swatch EXACTLY as it is in InDesign, and setting the CMYK values to match. As long as the swatch name is identical as the InDesign name it will output to the same plate.
  8. Find any remaining CMY color using Separations Preview (in the Window menu). All CMY must be converted to tints of black or your spot color.
  9. Convert Remaining CMY colors. Select an object filled by a CMY color, go to Select menu: Same: Fill Color to select all objects using that fill. Click your spot or black swatch to apply it to all these objects, and then use the Color Panel to adjust the tint of the swatch to appropriate levels. Repeat this process until no CMY color is left in the document.

Screenshot of PDF converted to 2 color in Illustrator, showing the relevant panels and menu selection.

It looks like a long process, but once you get used to doing it, it only takes a couple minutes per chart. Since I’m not an Illustrator expert there might be easier ways that I haven’t discovered, but I’ve looked and haven’t found anything better than this method, and it works pretty well.

Conclusion

If you need to convert a PDF to CMYK or Grayscale, using Acrobat Pro’s Convert Colors tool is the easiest way to do it. If you need to convert a PDF to black and one (or more) spot color, use Illustrator. Then place your file into InDesign and you’re all set!

Addendum: Placing multiple pages of a PDF into InDesign

I’ve mentioned this in other posts, but it’s worth mentioning again. InDesign only lets you place the first page of a PDF by default. To place any other page, you must enable the “Show Import Options” in the place dialog. This will bring up an intermediate dialog where you can specify any page or range of pages in the PDF.

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