ABCs of PDF explained!


PDF (Portable Document Format) is used by all to present and exchange documents as a file format. P Chellappan, Managing Partner, PM Digital Products, uses it extensively for his digital jobs. Experiencing the usage of it at every stage, he found that still not many understand PDF completely. In his view, PDF is still developing. He shared his experience in a presentation on PDF; in detail about its usage, to the members of The Printing Technologists Forum March 23, 2018.

What is PDF? Portable Document Format, is a file format used to present and exchange document reliably, independent of software, hardware or operating system. Invented by Adobe, PDF is now open standard maintained by the International Organisation for Standardisation (ISO). PDF can contain links and buttons, form fields, audio, video and business logic. They can also be signed electronically and are easily viewed using free Acrobat Reader software.

PDF Standards: PDF files meet ISO 32000 standards for electronic document exchange, including Special Purpose Standards like PDF/A for archiving, PDF/E for engineering and PDF/X for printing. It offers accessibility standards that make content more usable by people with disabilities.

PDF combines three technologies: a subset of the PostScript page description programming language for generating layout and graphics;a font embedding/replacement system to allow fonts to travel with the documents;; and a structured storage to bundle these and any associated content into a single file. It is called Carousel Object System. Carousal was the original code name for what later became Acrobat.

PDF Structure: A PDF file is a 7 bit ASCII file except for certain elements that may have binary content. The basic structure of a PDF file is Header, Objects 8 types, Cross Ref, and Trailer.

PDF Objects information permits direct objects embedded in another object and indirect objects numbered with an object number and a generation number defined between the obj and endobj keywords. They are true/false, Numbers Strings Names, Arrays, Dictionaries, Streams and Null which are interesting for Programmers. There is a PDF xref table containing information that permits random access to indirect objects.

The speaker then displayed on the monitor, aminimal PDF Programming, and font embedding methods.

Playing with PDF: With his indepth knowledge, Chellappan played certain combinations which took the audience to astounding interest to see what all can be done (‘played’) with PDF. He concluded by saying that PDF is still developing.

–D Ramalingam

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