Is there a way to modify the fpdf output, so the name can be changed according to input by user?

Question

I am writing a program that takes input from a user in a variable called client_name; the method output() of the class FPDF does not allow me to change the file name of the PDF according to the client_name entered.
I've got the following code line to output my pdf file:

pdf.output(client_name".pdf ")

but it produces a syntax error.

Basically, I need that the file name of the PDF changes every time the client name change, please help.

Thanks

I've already tried entering this line pdf.output(client_name".pdf "), hoping the pdf filename will change according to client name.