As with other pairs of misused words, I imagine the confusion stems from the similar appearance and sound of each of these adjectives. Add to that a failure to distinguish written English from spoken English, and you’ve got a great foundation for less effective writing. Whatever the cause, definite and definitive have related but clearly different meanings. Definite means clear or certain. Definitive means complete and authoritative.
Consider the example sentence in the cropped graphic above. The writer uses the words definite and definitive correctly. Test results can be both clear and certain, and a report can be both complete and authoritative.
Swapping the use of those two words could work but would produce a different effect. A report can be clear and certain, and test results can be complete and authoritative. But the sentence describes a process in which the test results are an input and the report is an output. Although clarity can create authority (or at least the appearance of it), authority does not always create clarity.
More effective technical writing follows from more effective use of language, and that demands precision. So be definite about your use of definitive. Understand the differences between apparently similar words, and you will present your message more effectively. And that will represent you and your brands more effectively, which is what every serious technical writer wants.