Sounds like an Acrobat question... perhaps the last designer tweaked the settings last year... have u made a pdf of that document to see if the settings you have create the same file size? If it doesn't then clearly something is different.
Are you sure that you aren't using a different PDF preset than before?
The usual answer relates to PDF metadata, but you can try Audit Space Usage in Acrobat as a tool to try to help narrow it down.
Does the size really matter?
Size does matter as when we upload the mag, normally on a finished folder size of around 300mb, it takes around an hour (not very good internet singal here), but on a finished folder size of around 1gb, it can take around 5 hours! How would I audit space in Acrobat and what would it do?
How would I audit space in Acrobat and what would it do?
Assuming you're using Acrobat X Pro, it is hidden in the FIle > Save As > Optimized PDF... dialog box, in the upper-right corner, "Audit space usage...".
It will tell you what objects in the PDF are using the space, by type of object. This should especially be useful if you have two PDFs to compare, as it sounds like you do.
That is very helpful, I will check it out. We now have a technician coming in at the end of next week to fix the issue.
Many thanks for your advice.