This is quite simple actually. You,re issue is that EPDM can take up to 10 000 characters if my memory is right.
But it communicates with word or excel through the custom properties, The custom properties in office allow up to 256 characters. There is no way, that i know of, around that. So you can right 1000 chars in the data card, but nly 256 are transfered in office doc, and then the data card will also reflect this 256(updates with what is stored in the file's properties so it looses the rest)
I know there is a lot of info, here is some : http://www.javelin-tech.com/blog/2013/04/epdm-multi-line-edit-box-character-limit/#.WH0iyVUrJFE
Which is why I'm moving towards using XML files to remove these types of limitations