Please note that this only applies to older versions of the Plesk control panel on the linux operating system as windows does this automatically.
When you set up an SSL certificate on a domain set up through Plesk then automatically when viewing your website over this SSL cert (i.e. https://domain.com rather than http://domain.com) then the webserver will look for these files in the httpsdocs folder rather than the httpdocs folder for security.
If you have an SSL cert set up on one of your domains you might prefer to use the standard httpdocs folder when using the SSL cert rather than the httpsdocs folder.
This can be done on some of the newer versions of Plesk under:
Domains >> domain name >> Setup >> Enable the "Use a single directory for housing SSL and non-SSL content" option here.
As the above has only been available in Plesk recently here is the old, command line, method of doing this:
If you have a Linux VPS you can do this by connecting to your VPS via SSH (this can be done under Virtuozzo, from your own linux computer, or using a downloadable program like Putty for Windows users). Once you have logged in you can navigate to the domain's root directory by:
#> cd /var/www/vhosts/*domain.com*
where *domain.com* is the domain name in question.
Once in this directory you can create the symlink using the following commands:
#> rm -rf httpsdocs
This deletes the current httpsdocs folder so make sure there is nothing in it you need
#> ln -s httpdocs httpsdocs
This creates a 'symlink' which basically links the httpsdocs folder directly to httpdocs making it the one and the same.
#> chown -h USER.psaserv httpsdocs
This sets the ownership of the symlink to match the ownership of the httpdocs folder. USER is the user for the domain in question.