Website description in a different file from index.php

Hello all,
I’ve a website with wordpress configured in a directory called ‘main’. So the web-address is “mydomain.com/main”. However I’m thinking of creating a ‘Welcome Page’ in my home dir, and put a button in that page as ‘Please Enter’ to link it to mydomain.com/main.
I know a trick to achieve this by keeping two homepages linked like index1.php and index2.php but that is not possible since I’m using WordPress (seemingly that does not allow any index file to have a name like index2.php).
The problem is that the keyword density may be very less on my welcome-page, so I was wondering if it is possible in any way to
have the website description, along with meta keywords etc. in a different file (other than the welcome page) in the home dir, such that the search engines would be told to search that file (say metadescriptions.php) for the keywords etc. If it is possible to achieve this in any way by any code, please let me know.

I hope I’ve made myself clear about this. And yes, I’m a beginner in php codes, so kindly detail out the necessary steps.

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