What is a PDF file?

The acronym PDF stands for Portable Document Format, which is a file format that resulted from a specific need in the 1990s for document presentation without requiring further application software or hardware, or a specific operating system. PDF has amassed great popularity among millions of users and with its steady stream of innovations; it is expected to stay as one of the top preferred file formats.

PDF history

PDF was created by Adobe Systems in 1993 as competition to other file formats such as Common Ground Digital Paper and Envoy. It was not until 2008, however, that Adobe published a Public Patent License for PDF (that on July 1st was published as ISO 32000-1 by the International Organization for Standardization.

PDF was originally a proprietary format until it was dropped in 2008 to become an open standard. It was introduced to make document sharing amongst computers and various operating system platforms easier.

Developed by Adobe co-founder John Warnock in 1991 as The Camelot Project and by 1992 transformed into the structure of PDF file that is well known today.

PDF files, based on the PostScript language on which they were developed, contain a complete description of fixed-layout flat documents which includes the texts, fonts, vectors, raster images, and other information included to allow for display as is.

PDF file structure

Officially, the PDF is a 7-bit American Standard Code for Information Interchange (ASCII) type of file, excluding binary content. The structure of a PDF file is quite extensive but can be broken down into four basic parts, which entail: header, body, cross-reference table, and trailer.

The header is the first line of a PDF file which allows the user to recognize the version number of the used PDF specification in said document. A simple use of the hex editor will give you the information.

Body

A subset of a COS (Carousel Object Structure) format outlines the data and includes certain symbols that encode streams, dictionaries, comments, arrays, strings, numbers, and more. The body is where all relevant information is held that must be presented to the user. A PDF file has the possibility to contain a plethora of data such as the following: multimedia elements, web page links, interactive elements, signatures, text, graphics and more.

Cross-reference table

The cross-reference table is useful for locating specific objects within a PDF file without the need to read the whole document. It contains a specific reference to each and every object, represented by a 20 bytes long entry. Easily display the cross-reference table by opening any PDF file with a text editor and scrolling all the way down. A bit of previous knowledge of coding symbols is advised in order to read and understand the full information displayed.

Trailer

The trailer will help the application being used to read the PDF file find the cross-reference table. PDF readers begin reading the file from this exact part of the document, the end. Precise PDF structure will vary from document to document and will also change if the file is updated but the basic parts remain true.

PDF file layouts

There are two layouts to a PDF file: non-linear and linear. They are also referred to as non-optimized and optimized (or web optimized PDF files) respectively. Non-linear PDF files have the advantage of consuming less disk space but are slower to access. Linear PDF files will open quickly and can be read in most web browser plugins without downloading the complete file. You can optimize a PDF file using PDF Multitool. The PDF document structure is characterized by a combination of three technologies:

A PostScript page description programming language subset that is used for layout and graphics generation.
A font-embedding program that allows fonts used in the document to travel with the file unchanged.
A storage system that binds all elements and associated content into one file and compresses data where it sees fit.

To access a PDF file the use of a program called Adobe Reader is required.. It is a free distributed application by Adobe Systems which allows users to access and share PDF files with any person(s) who can then view or print the file on any system. Adobe Reader is available on Windows, Mac, Unix, Linux, AIX, HP/UX, and Solaris operating systems as well as on mobile devices that run Palm OS, Pocket PC, or Symbian OS.

PDF files can be created using ByteScout or online but as its use over the years broadened, many applications or programs have adopted PDFs by allowing its users to be able to save, import, and export their documents in PDF format as well as change the PDF format history.

There are several tangible reasons why you should opt for the usage of PDF, some include it being multi-dimensional such that it allows for the integration of various content types i.e – text, images, and vector graphics, videos, animations, audio files, 3D models, interactive fields, hyperlinks and buttons most suitable for presentations and portfolios. Another reason will be that it is compact meaning regardless of the unlimited amount of content that a PDF file can contain they are easily compressed into a suitable file size for smooth sharing while retaining full control over the level of image quality.

A very important reason to use PDF is that it is secured, offering various levels of security available for users to pick from. The graphic integrity of PDF files is unmatched, it displays the exact format or structure and same content even regardless of which operating system is being used to access the file. It is also very convenient to use.

PDF files are also faced with certain limitations, although not very severe — one of which is the fact they are particularly hard to edit and extracting information from the PDF file structure sometimes oppose an unnecessary challenge, files often need to be converted into word formats in order to be able to make any edits on them. It is also often difficult to copy a fragment of a PDF file.

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