Do I have to install composer on the Linux server? sure, you must run composer install on server rather than uploading your vendor directory.

Do I need to re-install again on the Linux server? You do need to install using composer.

Thank for your suggestion. But currently, I cannot have SSH access. Is there another way?

Are you sure that I have to do this? I do not need to install composer on Linux server or anything. And It ran successfully after I uploaded some new components in the folder vendor that the "dompdf" depends on.

Why not just uploading the files of dompdf like your own files? Should still work.

You could use something like:

https://www.deployhq.com/ http://beanstalkapp.com/

I've used both of them in the past, they're pretty handy

Yes it should work even if you upload the vendor folder, but is not the recommended approach, what you need to do is download composer on linux server and running composer install, if you don't have ssh access you could use a php shell like script that runs composer, eg. using shell_exec().