It is one of those urban myths of publishing, that you frequently need to outline fonts. The truth is that you should almost never have to outline fonts. However, some print service providers and others insist that they won’t accept a PDF file unless the fonts have been outlined.
The truth is that InDesign always embeds fonts in the PDF if the font vendor’s End User License Agreement says you can. Sometimes users think they can get around restrictions on sharing fonts with others by converting text to outlines.
Converting text to outlines does not sidestep the provisions of the font vendor’s EULA. In fact, while some some font vendors’ licensing allows conversion of text to outlines, many expressly forbid it.”
Here are some other good reasons not to outline fonts:
1. The outlining of text will degrade the typographic quality of the text. The glyphs are turned into normal graphics which lack the intelligence that fonts have in displaying or printing text, particularly on lower resolution devices. Fonts have hinting built in, which makes them look good at low resolution. This is lost when you outline type.
2. Certain attributes will be lost when outlining because they are not part of the font itself, but are applied by InDesign. Try adding these features to your InDesign type – underlining, strikethrough, bullets applied with the Bullets & Numbering feature, or footnotes. Then select the text and choose Type > Create Outlines. Those attributes will disappear.
3. The PDF will no longer be editable, in case you need to do a last minute correction of a typo.
Nevertheless, some people do want all the text converted, and they find themselves up a creek because Type > Create Outlines doesn’t always give them what they want. Specifically, paragraph rules (rule above/below) disappear. Bullets and numbering disappear. Underlines and strikethroughs disappear. All kinds of stuff disappears, and that’s not good.
Fortunately, there is a better way to convert text to outlines.
Acrobat Pro DC to the Rescue. Simply run a Preflight fixup on a PDF in Acrobat Pro DC to outline the fonts. This is a new fix-up which will not be found in Acrobat Pro XI or earlier so you’ll need the latest Acrobat version.
Here’s how to use this new method:
1. Create your PDF file as usual. You don’t have to choose a particular preset, or select Acrobat 4 compatibility. The method is even compatible with the PDF/X-4 PDF preset which retains transparency and supports color management.
2. Open the PDF file in Acrobat Pro DC. Open the Print Production panel and open Preflight. In the Search field at the top right, search for “outline”. This selects the “Converts fonts to outlines” fixup.
3. To run the fixup, at the bottom of the dialog box, click Analyze and Fix, and save the file under a new name.

Fonts are now outlined. This method is faster, and keeps your PDF file smaller. It works with all PDF presets. Furthermore, if you needed to do this multiple times, you can create a Preflight Droplet to batch process your PDF files.
Summarised from several posts by, and with special thanks to, David Blatner at InDesign Secrets.