“Everything that has a beginning, has an end. I see the end coming.” — The Oracle
To first provide some background, I started to work at Adobe right before we invented CID-keyed fonts. The first desktop (aka non-printer) deployment of CID-keyed fonts was in the form of “Naked-CID fonts” in 1993 or so, which required ATM (Adobe Type Manager) to be installed. While such fonts were available for Macintosh and Windows OSes, Naked-CID fonts for the latter OS were incredibly short-lived and therefore rare, and were subsequently replaced with OpenType/CFF fonts in the late 1990s. Naked-CID fonts for the former OS were replaced by “sfnt-wrapped CIDFonts” (aka “sfnt-CID fonts”) in the mid-1990s, and also required that ATM be installed. Adobe Tech Note #5180, entitled “CID-Keyed sfnt Font File Format for the Macintosh,” details the sfnt-wrapped CIDFont format, which is specific to Macintosh due to its use of a resource fork.
With that stated, fonts are among the most perpetual and resilient of digital resources, meaning that discontinuing support for legacy font formats cannot be done quickly, and many years must pass before it can be realistically considered.
To get to the point of this article, we (Adobe) recently announced that CIDFont support in our Creative Cloud apps—such as Illustrator, InDesign, and Photoshop—will be discontinued starting from the next major release in 2019. The CC 2019 apps that were released in October of 2018, along with any dot releases thereof, will continue to support CIDFonts. Although sfnt-wrapped CIDFonts were obsoleted by OpenType/CFF fonts approximately 20 years ago, a non-trivial number of such fonts were distributed over many years. This effectively means that a non-zero number of customers will be affected, including myself. If you are an affected customer, the prudent thing to do is to start making preparations accordingly.
In other words, the proverbial writing has been on the wall for years, so this announcement should not be construed as a shock by any stretch of the imagination.
To put this announcement into an actionable and practical perspective, Naked-CID fonts and sfnt-wrapped CIDFonts have serious disadvantages when compared to OpenType/CFF fonts, in particular, the lack of Unicode support, which is a big deal for modern environments. In essence, these legacy font formats are restricted to legacy encodings, such as Shift-JIS for Japanese, are not cross-platform, do not work in mobile OSes, and have limited typographic features and functionality. Of course, CIDFont resources will continue to serve as one of the source files for CID-keyed OpenType/CFF fonts, at least when using AFDKO‘s makeotf to develop such fonts.
For more information about these legacy font formats, I encourage you to read this pp 387 through 393 excerpt from Chapter 6 of CJKV Information Processing, Second Edition.