The Portable Document Format (PDF) is an ISO standard electronic file-format. Question about PDF can be about reading, converting, creating and editing such files.
The PDF format was first developed by Adobe Systems in 1991 and is based on PostScript. It has evolved over time and is now an international standard (ISO 32000-1:2008).
The PDF format allows for quite accurate rendering of specific layouts. This can lead to problems when viewing PDF files on screens smaller than the original intended page layout (Letter or A4 size).