.PDF File Format – Versions

PDF 1.0

The first version, with Acrobat 1.0 in 1993. It had the file structure that every later version kept, pages in a page tree, content streams with almost all of the operators, Type 1 and Type 3 fonts with the standard 14, the device colour spaces and Indexed, images with LZW, RunLength, CCITT fax and DCT (JPEG) compression, and ASCII85 and ASCIIHex to keep files 7-bit. For navigation it had text notes, links, bookmarks and thumbnails.

PDF 1.1

With Acrobat 2.0, in 1994:

• passwords and encryption, RC4 with 40-bit keys, and the file identifier ID;
• files may hold raw binary data;
• device-independent colour: CalGray, CalRGB and Lab, rendering intents and ri, and the colour operators CS, cs, SC, sc;
• TrueType fonts (FontFile2);
• article threads, actions (GoTo, GoToR, Launch, Thread, URI), named destinations and the three bounding-box views (FitB, FitBH, FitBV);
• presentation timing and transitions on pages;
• the compatibility operators BX and EX.

PDF 1.2

With Acrobat 3.0, in 1996:

• interactive forms (AcroForm), widget annotations, and FDF for form data;
• Flate compression and the PNG predictors;
• Unicode text strings (UTF-16BE);
• composite fonts: Type 0, CIDFonts and CMaps, and ToUnicode; compact Type 1 fonts (FontFile3, Type1C);
• Separation colour spaces, tiling patterns, sampled functions, halftones, transfer functions, and graphics state dictionaries with gs;
• marked content (BMC, BDC, EMC, MP, DP) and SCN, scn;
• the name dictionary and name trees, appearance streams, sound and movie annotations and actions, more actions (Hide, Named, SubmitForm, ResetForm, ImportData) and viewer preferences;
• external streams, # escapes in names, OPI;
• linearized files for fast web view.

PDF 1.3

With Acrobat 4.0; Adobe’s reference for it is dated 2000:

• digital signatures and signature fields;
• JavaScript actions;
• embedded files and file attachment annotations;
• new annotations: FreeText, Line, Square, Circle, Highlight, Underline, StrikeOut, Stamp, Ink, Popup, TrapNet;
• smooth shading: seven shading types, shading patterns and sh; exponential, stitching and PostScript calculator functions;
• ICCBased and DeviceN colour spaces;
• masked images (Mask) and alternate images;
• CID-keyed CFF fonts (CIDFontType0C);
• logical structure, page labels, Web Capture, and the prepress page boundaries BleedBox, TrimBox and ArtBox;
• the public-key security handler adbe.pkcs7.s3.

PDF 1.4

With Acrobat 5.0, in 2001:

• transparency: blend modes, opacity, soft masks, transparency groups, and soft-mask images;
• JBIG2 compression;
• RC4 keys of 40 to 128 bits (V 2, R 3) with more permissions, and adbe.pkcs7.s4;
• XMP metadata streams;
• Tagged PDF and MarkInfo, the document language Lang, and accessibility features such as ActualText;
• output intents, page-piece dictionaries, printer’s mark annotations and the Squiggly annotation;
• the catalog’s Version, the embedded files name tree, and document-level additional actions;
• reference XObjects, and XFDF and whole-PDF form submission.

PDF 1.4 added no content stream operators: transparency is set through graphics state dictionaries.

After 1.4

PDF 1.5, with Acrobat 6.0 in 2003, added cross-reference streams and object streams, which let objects be stored compressed inside other objects and change how a reader finds them. That is a different format, PDF 1.5 to 2.0, described separately. A PDF 1.4 reader cannot open a file that relies on those streams; many 1.5 and later files are written so that it still can, or use only the features of 1.4 with a later version number. See the PDF family page for the versions as a whole.

Standards based on these versions

• PDF/X-1a:2001 (ISO 15930-1) – for print exchange: CMYK and spot colours only, fonts embedded, no encryption; based on PDF 1.3
• PDF/X-3:2002 (ISO 15930-3) – for print exchange with colour management; based on PDF 1.3
• PDF/A-1 (ISO 19005-1:2005) – for long-term archiving: everything embedded, no encryption, XMP metadata; based on PDF 1.4