Searching for “Adpdf9 Ppd Download Mac” yields dozens of suspicious pages.
The context of the "Mac" in this search query is vital. The Macintosh has long been the preferred platform for creative professionals, and during the era of Mac OS 9 and the early iterations of OS X, the workflow was rigid. Designers did not simply hit "Print" to create a PDF as they do today. Instead, they printed to a virtual printer using a specific PPD file. This generated a PostScript file, which was then manually fed into Acrobat Distiller to "distill" the final PDF. The "Adpdf9 Ppd" was the linchpin of this process. It allowed the designer to "print" to a digital file while maintaining the precise constraints required by commercial printing presses. It was a workaround for an operating system that didn't yet have native PDF support baked into its core.
Before searching the web, check if the file is already on your Mac.