A photo of a whiteboard or a printed page is often just legible enough to be frustrating. Adjusting the tones usually fixes it.
Text is readable when it separates clearly from its background. Most unreadable photos of text are not out of focus, they are low contrast, so the letters and the paper sit at similar brightness. Widening that gap does more than any sharpening.
Removing colour helps more than people expect. Whiteboards photographed under fluorescent light go slightly green or blue, and dropping to black and white removes that distraction entirely, leaving only light and dark.
Genuine blur cannot be fixed. If the camera moved or missed focus, the detail was never recorded and no adjustment recovers it. Retake it if you still can.
No. If the detail was not captured it cannot be restored. Low contrast can be fixed, blur cannot.
Often yes, especially for whiteboards and printed pages under artificial light.
No.