Page with .htm redirect to 500 internal server error in Joomla

Question

Whenever I tried to access any of my webpage through .htm extension, it leads to a 500 server error, although webpages are accessible without ant extension or with .html extension, this is important for me because some of my pages are linked with other websites with .htm extension and whenever a use click on those links, page redirect to 500 internal server error, i cannot remove those links, and cannot redirect them with .html extension

my website is http://www.gautampolymers.com

my .htaccess file is

# RewriteBase /

## Begin - Joomla! core SEF Section.
#RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the request is for something within the component folder,
# or for the site root, or for an extensionless URL, or the
#requested URL ends with one of the listed extensions
RewriteCond %{REQUEST_URI} /component/|(/[^.]*|\.(php|html?|htm?|feed|pdf|vcf|raw))$ [NC]
and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
>#

Answer 1

Joomla sorts out the .html extension itself.

I would suggest you create a new menu called hidden and then create a new menu item linking to the page you wish. Then simply link whatever you were trying to link to the new menu item, for example:

index.php/news

be sure to start you're link with index.php