Whether it is possible to create a folder that will contain user’s personal documents that can only be opened by the user and all other users of the Windows 7 on the same PC can not access it anyway?

Yes it is possible.

I will show you, how to create a folder with a lock sign on it, that can only be accessed the original user or author, no other user can access it, even it is not in My Documents folder.

For example, I have created a folder named The Customize Windows in E partition of my Windows 7 PC:

By right-clicking on the folder, select Properties and open the Security tab :

Now, click the Users other than you; click Edit:

Select the user group/user and fill the check box how much you will give access to the user.

You can allow only to read, not to copy or even not to access/open the folder. After restart or simply restarting the explorer.exe, when an unauthorized user wants to open the folder, he/she will get this:

In the above example, I have made all users to be denied by the System to access the folder.