I was opening my Programming C#, 3rd Edition ebook from O’Reilly in .CHM file extension with my Windows 7 and found that the file was just like blank pages. No text neither images. Like this one: This isn’t something I expected. I tried to click another chapter and nothing changes. Searching for the solution, someone said that I need to ‘unblock’ the file from the properties of the file. But, when I look at the properties there’s no such thing like ‘Unblock’ button.