Any document you come across in the course of research will have some element of bias baked into it.  Despite even their best efforts at neutrality, all individuals and all organizations have some level of bias that is then reflected in the words they say and the documents they write. 

As a researcher, your job is to be aware of the biases inherent in the information you find and try to understand how those biases may affect what the authors write and how they present it.

As a writer, your job is to try and avoid bias in your writing as much as possible.  You can do this by using inclusive language, writing objectively, and avoiding hyperbole and logical fallacies.  The resources below can help you with these aims.