PDF Page Size
Because PDF files are page-based, the underlying page size (or effective page size) matters - both for successful output to print devices and for reading on-screen.
The great majority of documents that are converted into PDF format are based on A4 or US Letter page size in Portrait orientation. This has a total height of 11+ inches or 300mm. If a computer screen displays at 100 pixels per inch the screen would need a resolution of at least 1100 pixels vertically to display the page, and even then it would be very difficult to read typical text at, say 12 point size. And many computer displays and most mobile devices (including tablets and phones) are less than 11 inches high so any entire page will be shrunk to fit the available screen space. Technical drawings (e.g. architectural drawings, circuit diagrams, 3D wireframes) can be even more difficult to decipher as they often include small fonts and fine lines, and may be generated on much larger underlying page sizes. This does not present a serious problem for print output, as long as the printing is carried out with at least 300dpi (dots per inch) or preferably 600-2400+ dpi.
There are a number of solutions to this problem, the most obvious of which is zooming. Most PDF readers support immediate zooming to page width, and this increases the font size viewed dramatically with the result that the text is easy to read - however, a downside of this is that the page then has to be scrolled vertically and maybe horizontally in order to read the entire text on a page. This in turn has some impact on the ease with which the user can read the document, particularly if it has many pages. For reference works, where small sections are referred to, this is not really a problem, but for fully reading and absorbing a long document, it is a limiting factor. The main alternative to zooming the page is for the source document to be arranged (designed to fit) on a smaller page size (e.g. A5 or one-half US Letter) and/or a landscape orientation used, and/or for the document to be created with larger font sizes.
In some cases (mainly for technical drawings) tiling can be used to generate a set of standard-sized pages that combine to form a much larger overall page. Tools to support tiling are available as standard in some PDF creation and editing software.
Paper sizes and Page Orientation
In principle a document page can be any height and width, but for many documents there are standard sizes that correspond to widely available paper sizes and/or page size specifications. There are a very large number of paper size "standards" - see the Wikipedia Page Sizes article for full details, but the most widely used for commercial documents are based on the ISO 216 standard (itself developed from the German DIN 476 standard) and the US paper size standards (e.g. US Letter, US Quarto etc.). The ISO format paper sizes are named A0, A1 etc., where each successive size is half the size of the previous page size.
The ISO standards provide for some of the most commonly used paper sizes as shown below:
|A0||33-1/8 x 46-13/16 in||841 x 1188 mm||84.1 x 118.8 cm|
|A1||23-3/8 x 33-1/8 in||594 x 841 mm||59.4 x 84.1 cm|
|A2||16-1/2 x 23-3/8 in||420 x 594 mm||42.0 x 59.4 cm|
|A3||11-3/4 x 16-1/2 in||297 x 420 mm||29.7 x 42.0 cm|
|A4||8-1/4 x 11-3/4 in||210 x 297 mm||21.0 x 29.7 cm|
|A5||5-7/8 x 8-1/4 in||148 x 210 mm||4.8 x 21.0 cm|
The most widely used US paper size is that which equates to ISO/DIN A4. This is the US Letter page size, which is 11.5 inches x 8.0 inches.
Books and magazines that are published in print as paperback or hardback publications tend to have a much wider range of page sizes, although rarely are very large page sizes used. Typical (trimmed) sizes for many books are 8x10 inches (254x203mms) and 6x9 inches (229x152mms). Note that for screen display it is normal to either trim the print-production version of a PDF file to the final page size (reducing the overall page size of the output PDF) and/or to remove the print production marks (trim/crop, color bars, registration, information or other printer marks) to avoid these appearing on the final displayed PDF. Some PDF readers will automatically hide such content, just showing the document page rather than including the surrounding print mark-up.
Where a page has a standard size that is not square, as is the case with most documents, the orientation of the page becomes important. Typically pages are shown in Portrait orientation, which means that the shorter dimension provides the horizontal and the longer provides the vertical. However, most computer screens are wider than they are high and cannot be physically rotated, so displaying pages in portrait orientation can result in only part of a page being displayable at any one time. In most instances vertical scrolling of the page resolves this issue, but for some documents it is preferable for the document to be rotated through 90degrees into so-called "landscape" orientation. With mobile devices this is less of an issue as the device can usually be manually rotated when necessary or preferred. A bigger issue arises with mixed-orientation, where some pages are in portrait and some in landscape orientation. PDF readers on desktop/laptop devices should provide a tool to rotate the current page through 90degrees clockwise or counter-clockwise, in order to enable the user to read the relevant page(s). However, it is preferable when creating PDFs for screen viewing to create pages that are all in the same orientation and all the same size or close to the same size.