How to deny the web access to some files?

Solution 1:

You could use Files/FilesMatch and a regular expression:

<Files ~ "\.txt$">
    Order allow,deny
    Deny from all
</Files>

This is how .htpasswd is protected.

or redirect any access of .txt to a 404:

RedirectMatch 404 \.txt$

Solution 2:

From the Order documentation section:

Keywords may only be separated by a comma; no whitespace is allowed between them.

So the following is incorrect:

<Files File.txt>
Order allow, deny
Deny from all
</ Files>

The following is (more) correct

<Files "File.txt">
Order allow,deny
Deny from all
</Files>