I took a new Server and After install my PHP files, I found My PDF file functionality not working. So I was very much worried about how to fix the Dompdf not working in my New Server. I search in google and many more blogs site, finally I found the solution. So Solution is In the new Server we have to Install mbstring extension. If you have WHM access then you can do your self by using the below steps. See that image below to figure it out easily.
step1-Login WHM and search for easy Apache4
Step2- Click PHP Extensions that you can see above image.
Step3-Install mbstring module as per your PHP version.
step4- Save It.