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The Portable Document Format (PDF) is a file format used to present documents in a manner independent of application software, hardware, and operating systems. Each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, graphics, and other information needed to display it.
PDF was developed in the early 1990s as a way to share computer documents, including text formatting and inline images. It was among a number of competing formats such as DjVu, Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe's own PostScript format. In those early years before the rise of the World Wide Web and HTML documents, PDF was popular mainly in desktop publishing workflows. Adobe Systems made the PDF specification available free of charge in 1993. PDF was a proprietary format controlled by Adobe, until it was officially released as an open standard on July 1, 2008, and published by the International Organization for Standardization as ISO 32000-1:2008, at which time control of the specification passed to an ISO Committee of volunteer industry experts. In 2008, Adobe published a Public Patent License to ISO 32000-1 granting royalty-free rights for all patents owned by Adobe that are necessary to make, use, sell, and distribute PDF compliant implementations.
- A subset of the PostScript page description programming language, for generating the layout and graphics.
- A font-embedding/replacement system to allow fonts to travel with the documents.
- A structured storage system to bundle these elements and any associated content into a single file, with data compression where appropriate.
- PDF contains tokenized and interpreted results of the PostScript source code, for direct correspondence between changes to items in the PDF page description and changes to the resulting page appearance.
- PDF (from version 1.4) supports graphic transparency; PostScript does not.
- PostScript is an interpreted programming language with an implicit global state, so instructions accompanying the description of one page can affect the appearance of any following page. Therefore, all preceding pages in a PostScript document must be processed to determine the correct appearance of a given page, whereas each page in a PDF document is unaffected by the others. As a result, PDF viewers allow the user to quickly jump to the final pages of a long document, whereas a PostScript viewer needs to process all pages sequentially before being able to display the destination page (unless the optional PostScript Document Structuring Conventions have been carefully complied with).
Boolean values, representing true or false
Strings, enclosed within parentheses (
(...)), may contain 8-bit characters.
- Names, starting with a forward slash (
Arrays, ordered collections of objects enclosed within square brackets (
Dictionaries, collections of objects indexed by Names enclosed within double pointy brackets (
Streams, usually containing large amounts of data, which can be compressed and binary
- The null object
- a dictionary
- an offset to the start of the cross-reference table (the table starting with the
- and the
%%EOF end-of-file marker.
- a reference to the root object of the tree structure, also known as the catalog
- the count of indirect objects in the cross-reference table
- and other optional information.
ASCII85Decode a filter used to put the stream into 7-bit ASCII
ASCIIHexDecode similar to ASCII85Decode but less compact
FlateDecode a commonly used filter based on the deflate algorithm defined in RFC 1951 (deflate is also used in the gzip, PNG, and zip file formats among others); introduced in PDF 1.2; it can use one of two groups of predictor functions for more compact zlib/deflate compression: Predictor 2 from the TIFF 6.0 specification and predictors (filters) from the PNG specification (RFC 2083)
LZWDecode a filter based on LZW Compression; it can use one of two groups of predictor functions for more compact LZW compression: Predictor 2 from the TIFF 6.0 specification and predictors (filters) from the PNG specification
RunLengthDecode a simple compression method for streams with repetitive data using the run-length encoding algorithm and the image-specific filters
DCTDecode a lossy filter based on the JPEG standard
CCITTFaxDecode a lossless bi-level (black/white) filter based on the Group 3 or Group 4 CCITT (ITU-T) fax compression standard defined in ITU-T T.4 and T.6
JBIG2Decode a lossy or lossless bi-level (black/white) filter based on the JBIG2 standard, introduced in PDF 1.4
JPXDecode a lossy or lossless filter based on the JPEG 2000 standard, introduced in PDF 1.5
AcroForms (also known as Acrobat forms), introduced in the PDF 1.2 format specification and included in all later PDF specifications.
Adobe XML Forms Architecture (XFA) forms, introduced in the PDF 1.5 format specification. The XFA specification is not included in the PDF specification, it is only referenced as an optional feature. Adobe XFA Forms are not compatible with AcroForms.
- HTML Form format (HTML 4.01 Specification since PDF 1.5; HTML 2.0 since 1.2)
- Forms Data Format (FDF)
- XML Forms Data Format (XFDF) (external XML Forms Data Format Specification, Version 2.0; supported since PDF 1.5; it replaced the "XML" form submission format defined in PDF 1.4)
- PDF (the entire document can be submitted rather than individual fields and values). (defined in PDF 1.4)
- to save the PDF document along with modified form and/or annotation data
- import form data files in FDF, XFDF and text (CSV/TSV) formats
- export form data files in FDF and XFDF formats
- submit form data
- instantiate new pages from named page templates
- apply a digital signature to existing digital signature form field
- create, delete, modify, copy, import, export annotations
- Text stored as content streams (i.e., not text)
- Vector graphics for illustrations and designs that consist of shapes and lines
- Raster graphics for photographs and other types of image
- Multimedia objects in the document
- PDF 1.7 
- PDF 1.6 ()
- PDF 1.4 ()
- PDF 1.3 ()
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