How can I stop my PDF from optimising when saving combined PDFs?

[Kaperberry]

I am combining several PDFs together in Acrobat, including some very high-resolution maps for printing.  When I go to save the combined PDFs, however, the file is automatically  'optimised for fast web viewing', and the resulting document is half the file size of the originals which makes me worry that I'm losing resolution.  Is there a way to save the combined pdf such that I don't lose file quality?  

[JR Boulay · Accepted solution]

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[Kaperberry]

Thankyou!  The 'save as pdf portfolio' option didn't produce what I needed so I unticked it, and the resulting document seems to be what I need.  I did lose some file size, although nowhere near what I was losing before when the file was being 'optimised'.  I think the file size reduction was due to the compression, which I'm hoping does not mean I have lost file quality/resolution.