Acrobat_Color_LayerAcroColor is an HFT that allows you to access the AcroColor engine (ACE), which controls color profile management for Adobe Acrobat. Plug-ins can import the AcroColor HFT to use the color management methods.
 AS_LayerThe Acrobat Support (AS) layer of the core API provides a variety of utility methods, including platform-independent memory allocation and fixed-point math utilities. In addition, it allows plug-ins to replace low-level file system routines used by Acrobat (including read, write, reopen, remove file, rename file, and other directory operations). This enables Acrobat to be used with other file systems, such as on-line systems.
 COS_LayerThe Cos layer provides access to the low-level object types and file structure used in PDF files. PDF documents are trees of Cos objects. Cos objects represent document components such as bookmarks, pages, fonts, and annotations, as described in Section 3.6, "Document Structure", in the PDF Reference.
 PDFEdit_LayerThe PDFEdit API provides easy access to PDF page contents. With PDFEdit, your plug-in can treat a page's contents as a list of objects rather than manipulating the content streams marking operators.
 PD_LayerThe Portable Document (PD) layer of the core API (also called PDModel) is a collection of object methods enabling plug-ins to access and manipulate most data in a PDF file.
 PDSEdit_LayerPDF files are well known for representing the physical layout of a document; that is, the page markings that comprise the page contents. In addition, PDF versions 1.3 and later provide a mechanism for describing logical structure in PDF files. This includes information such as the organization of the document into chapters and sections, as well as figures, tables, and footnotes.