OER Textbooks

I am in charge of reviewing online and hybrid courses for accessibility. Recently I reviewed a math course, Math 10, Nature of Math that is being offered hybrid. The instructor is using an OER (Open Educational Resources - free) PDF textbook that is also available in a Word doc version, and an older edition is available in print form for a small fee. Unfortunately the PDF and Word versions are not accessible, and obviously the work to make them accessible would be extremely time consuming. The publisher (a math teacher) is offering the text for free, so there is not the potential loss of financial gain for the publisher if he does not make his book accessible. 

Usually, it is not on my radar to be looking at textbooks, but as instructors are using more online digital textbooks and other online content, it becomes more problematic to clear a course for accessibility compliance. In a situation such as this, is it advisable to treat this PDF as any other print textbook, meaning that a blind student would need to go through the accommodation process in order to access it?