Cutting Off PDF

I am exporting PDF's and suddenly it is cutting off part of the design on the export...it used to work great but this is a new thing.  Any ideas??  It is killing me not knowing if it is a setting or what but if I export a 21' x 4' design for example, I will open it and it will be 16' x 4' - there does not seem to be a pattern or anything, sometimes it cuts length, sometimes width.  Any help would be amazing!!