hi all i am interested to make a program that will read the data from webpage using client.read() but i want to put the main webpage with much better design on SD card and access it after the login screen.
You can't READ a web page.
Is your Arduino supposed to be a server? That is the only situation where reading from an SD card makes sense. If that is the case, the server sends an HTML file to the client (browser).
what i want is to save the RAM and the ROM by making a small code for only checking login and then the main page from SD.
You can save RAM or ROM, not both.
What is your problem with serving HTML data from an SD card?