If I edit multiple files outside of Arbortext and then open in Arbotext I get extra line feeds and tables don't display why?

It appears that the document has context errors, and/or the document is using the default stylesheet, rather than stylesheet written for the document type

A text editor doesn't distinguish between tags, attributes, PIs etc. and text, so you can easily invalidate markup. Could've been a table tag in this case.

Also need to check text editor Save encoding and line break options.

You may also want to check the doctype. I know we've had issues were someone tried editing outside of Arbortext and messed the doctype up so that when it was pulled back in Arbortext couldn't resolve to the correct DTD.