Starting with version 5.0, Liferay's Document Library includes a diff tool to can compare text differences between two file versions.
Invoking Comparison #
When editing or viewing a file take a look at the "Version History" tab; if you click on the "Compare Versions" button without selecting any version, the two most recent versions will be compared; if you select just one version, this selected version will be compared to the most recent one; if you select two versions, these two versions will be compared.
The result is shown in two columns, the first column shows the oldest version of the file and the second column shows the newest version of the file. Letters with a red background and a line in front of them means that they were deleted, letters with a green background and underlined means that they were added. Grey lines aren't part of the file, they are just shown to align the differences and to give a better understanding of the context.
Comparable File Extensions #
The diff tool will appear only if the file in question has a comparable file extension, this way, users won't be allowed to compare binary files. You can set them in portal.properties:
Comparing Binary Files #
Some files like .doc, .odt and .rtf can have their text compared. In order for this to happen you need to turn on the Document Conversion with OpenOffice integration, they also need to be included in the property dl.comparable.file.extensions.