Nginx serve plain file if exists else serve /index.php

try this

server {
listen 80;
listen [::]:80;

root /home/www/example.com/htdocs;

index index.php;

server_name www.example.com;


location ~* ^[^\?\&]+\.(html|jpg|jpeg|json|gif|png|ico|css|zip|tgz|gz|rar|bz2|doc|xls|pdf|ppt|txt|tar|mid|midi|wav|bmp|rtf|js|svg|woff|ttf)$ {
    # First attempt to serve request as file, then
    # as directory, then fall back to index.php
    try_files $uri $uri/ /index.php;
    #try_files /favicon.ico =404;
}

error_page 404 /index.php;

location ~ \.php$ {
            add_header X-Is-PHP true;
            #try_files $uri =404;
            try_files /index.php =404;
            fastcgi_split_path_info ^(.+\.php)(/.+)$;
            # With php5-fpm:
            fastcgi_pass unix:/var/run/php5-fpm.sock;
            fastcgi_index index.php;
            include fastcgi.conf;
    }


}

changes

1) Added error_page 404 /index.php; so that all the requests not found on the server are redirected to index.php

2) Added "~ .php$" to location attribute.

3)If u want other PHP files to be interpreted as well, uncomment the line "#try_files $uri =404;" and comment the line "try_files /index.php =404;"

location / { if (!-e $request_filename) { rewrite ^/(.*)$ /index.php; } }