Your client seems to do everything possible to avoid reading. They will want to take any text away to avoid reading it in front of you.
They will ask a lot of questions. Often they may pretend that they have read the text but in fact they have not. This can lead to them signing documents that they have either not read or not understood.
Reading difficulties such as dyslexia don't just make reading hard, they make it really stressful. A person with dyslexia is often embarrassed of their difficulty because reading is incorrectly linked to intelligence.
Not all people who can't read have dyslexia. Some have not had the opportunity to learn in school and don't have much need to read in daily life (for example some older travellers). People with severe mental difficulties will also have trouble reading. But most people who struggle with reading don't have any mental issues at all and many are even highly intelligent.
Because of the emotional toll reading difficulties take, many dyslexic people have developed sophisticated coping strategies that include avoidance. Many rely on friends, colleagues or family members to read texts for them. Or they will ask lots of supplementary questions to help them get at what's in the text.
Many people who struggle with reading will improve greatly after specialist literacy teaching. But for many others literacy will be a lifelong struggle because of their dyslexia or other difficulty.
Accessibly formatted texts and more time for reading will help. But you should also give them alternatives to reading such verbal explanations, audio recordings, computer reading text out, using pictures, using colours, etc.