If you need to convert batch EML files to PDF, then you can do it manually and using an automated tool. Manual methods like thunderbird, in this select the folder, right-click and go to the ImportExportTool NG add-on then Export all messages in the folder, select PDF format and last Messages with attachments and Index. For this method, you need to add ImportExportTool NG add-on in thunderbird. This approach is simple but it takes a lot of time and is risky for data loss when you have huge data.
For fast and secure conversion, you can use reliable MailsDaddy EML to PST Converter, which is specially designed to convert EML files into many formats like PST, PDF, MSG, EMLX, and other formats. The tool supports bulk conversion, selective migration, and provides an easy to use interface for tech or non-tech users.

yes you can do with php. php has lot of third party pdf library's.