we have custom fields in Business Details
If we creat Invoice, in the screen all correct - custom field label and field value is on the same line.
But on the PDF label and value are on the separated lines, this is not correct.
You are responsible for performance of your custom themes. You should also be aware that Manager is not a what-you-see-is-what-you-get program. And screen views and PDFs are rendered by different engines. So they can produce different results. Often, different themes are necessary for screen view, PDF, and Print. Even then, you will find the PDF generator substitutes fonts (because of language translation issues).
I don’t think this has anything to do with the theme. It’s most likely has something to do with the text itself, maybe the place where you copied them placed extra special characters.
Either drop all of those custom field labels and values in a text editor that shows special characters or just type them in and see what happens.