DiffPDF is used to compare two PDF files.
By default the comparison is of the words on each pair of pages, but comparing character by character is also supported (e.g., for logographic languages).
And there’s also support for comparing the pages by appearance (for example, if a diagram is changed or if a paragraph is reformatted, or a font changed). It is also possible to compare particular pages or page ranges.
When the Compare button is pressed, DiffPDF does a high-speed scan of every pair of pages. To make the scan as fast as possible DiffPDF does a very rough check of each pair of pages—so it is possible that it identifies some false positives (i.e., page pairs that are really the same). False positives are quite rare.
Although DiffPDF is a GUI program, if run from a console with two PDF files listed on the command line, DiffPDF will start up and immediately compare them in Words mode, or in Appearance mode.
- Words Comparison Mode (default mode) – performs a a smart text comparison word by word for each pair of pages. This mode is fairly liberal regarding whitespace and tries to ignore layout changes (within a page) insofar as possible. It also treats all hyphens (soft-hyphen, minus sign, etc.), the same, that is, as a plain hyphen. This mode is best for alphabetic languages like English.
- Characters Comparison Mode – performs a smart text comparison character by character for each pair of pages. This mode is liberal regarding whitespace at the ends of lines and tries to ignore layout changes (within a page) insofar as possible. It also treats all hyphens (soft-hyphen, minus sign, etc.), the same, that is, as a plain hyphen. This mode is best for logographic languages like Chinese and Japanese.
- Appearance Comparison Mode – can be used to detect changes in fonts, diagrams, or any other visual aspects. This mode is absolutely strict and compares each pair of pages pixel for pixel. By default this mode shows differences using highlighting just like the Words and Characters modes do. However, it is also possible to compare using composition modes which can be useful to detect very small and subtle differences that aren’t immediately apparent
- Zoning – designed to produce more accurate results (i.e., fewer false positives). Its main use is for pages that have tables or that mix alphabetic and logographic text, since these can cause the underlying Poppler PDF library to provide the page’s words mixed up.
- Page ranges – compare particular pages or page ranges.
- Margins – ignore any text that is above a specified top margin, below a specified bottom margin, left of a specified left margin, and right of a specified right margin.
Developer: Mark Summerfield
License: GNU General Public License v2.0
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