In order to download the GMAT 2018 official guide (pdf) for free, the aspirants would need to visit the official GMAT website (mba.com) in order to get notifications about the test.
GMAT 2018 official guide
Since GMAT there is no set date on which you can take the test, the GMAT official guide will be available for download on the website for the entire year. One does not need to register on the site in order to access this, just visit the link and download.
The guide or the handout contains all the required information about the GMAT examinations. Right from how to register, finding the centers, contact information of the centers, taking the examination, the kind of papers, information on downloading the previous papers, what to do with the GMAT scores, how to best utilize your scores, what to do if you wish to retake your GMAT, which institutes offer admissions based on GMAT etc.