What do “SDF” and “COS” stand for?
SDF (Structured Document Format) and COS (Carousel Object System; Carousel was a codename for Acrobat 1.0) are synonyms for PDF low-level object model. SDF is the acronym used in PDFNet, whereas COS is used in Acrobat SDK. In many ways, SDF is to PDF what XML is to SVG (Scalable Vector Graphics). Cos object system provides the low-level object types and file structure used in PDF files. PDF documents are graphs of Cos objects. Cos objects can represent document components such as bookmarks, pages, fonts, and annotations, etc. PDF is not the only document format built on top of SDF/Cos. FDF (Form Data Format) and PJTF (Portable Job Ticket Format) are also built on top of Cos. The SDF/Cos layer deals directly with the data that is in a PDF (or Cos based) file. The data types are referred to as SDF/Cos Objects. There are eight data types found in PDF files. They are arrays, dictionaries, numbers, Boolean values, names, strings, streams, and a null object. In order to retrieve or modify PD
