Since Office 2013, you will often see a yellow bar at the top asking you to Enable Editing. Unless you press this button, you cannot type anything or format any content. This may sound irritating, but it is a very useful feature. It safeguards your interests.
The reason is simple. Even today, many viruses travel through Office documents – as macros. These files arrive either through email, downloaded from Internet or copied from USB drives. In these cases, there is a great danger of the file infecting your PC. To prevent this from happening, these files are now opened in a special way. Here you can read the file but not edit it.
If you trust the source, you will have to click the Enable Editing button. Unless you want to edit it, don’t Enable Editing. Just read and take the required action.