The testing which can be performed in a document is known as Documentation testing and is part of non-functional software testing.

• Documentation plays very important role in the success of Software. If you have proper documentation of your project then you easily check the software requirement in the initial as well as final stage with the help of document(test case) then you compare expected result with actual result and essay to report the bug in bug sheet or related tool(Jira, Pivotal..).
• The important point is that documentation quality plays very important role to success the software.The documentation can be tested in a number of different ways to many different degrees of complexity.
• Documentation helps us to describe the software with the help of pictorial / written information such as BRS, Use case, Test case, Test scenario, RTM, Bug Report.. hence the testing of all the above mentioned documents is known as documentation testing.
• Documentation testing can start at the early stage of the software process and it can be useful to save the large amounts of time and money, If the documentation is not correct then there will be major and costly problems. hence the earlier defect found is less cost effective to be fixed.

Conclusion: Documentation testing required in the initial statge of software development to reproduce the issue in initial level.