I have a full set of drawings i'm working on, they range from lower ground floor up to roof level. I have each floor level Xref into each service drawing. A problem i'm having is when i PDF the drawings any drawing with lower ground Xref into it seems to take an age to open up, the file size becomes massive, and if i was to zoom or pan the drawing goes blank & i have to wait an age for it to come back.
 
A little information on the drawings is that the average size of these lower ground drawings is 700kb while the other floors range from 400kb to 1311kb yet are all still smaller when i pdf them.
 
 The lower ground xref is only 559kb yet all others are larger.
 
Can anybody offer any help/solution too why these drawings with the lower ground xref into them are so large when i PDF them?

When you Make them into PDF's what is your resoluton set to? Sounds like it is set to high i would back it down to normal or low. This will make it a little fater and a little smaller file size.  In your drawings have you purged out all your unused items, Layers, blocks, ect... that might help also.

The resolution has never been a problem & everything is purged from the drawing, the drawing and the xref are actually the smallest of the bunch yet are producing the biggest file size once PDF. :s ??