Border appears in PDF version of document


I’m trying to create a 4 page A5 booklet style document. The document was designed in Libre Writer and when printed from there prints fine, however, when I convert it to a PDF and print a black border or margin appears around each page page (with 2 pages on a sheet).

There is no border on screen or on print preview in Libre or Adobe, I have tried playing with the borders on Libre, but they are all off as well (except that ‘none’, on line type drop-down under format-page-border, keeps resetting itself to thin line but that shouldn’t make a difference as no border is selected).

Anyone know what I’m doing wrong or if there is a lower level format setting I’m missing, or maybe something in the conversion?

Help most appreciated.