Can a PDF be "fixed"?

Pdfs produced from CAD software can bog down Acrobat, CAD files can have many layers and curved lines can be constructed from a large number of points (nodes) which Acrobat considers lines and attempts to correctly render (I believe). You may see some improvement by running the Acrobat preflight fixup "Convert smooth lines to curves" this should reduce the number of nodes by applying bezier curves where possible. This fix is also available as an option when saving as an optimized pdf, although I don't know if the tools are identical, (try both ways). You could also flatten the pdf layers and discard invisible layers (also an option when saving as an optimized pdf), although layers may be important to you. One user has reported improvement when the accessibility preference "Enable assistive technology support" is turned off. 

Edit, these suggestions assumes Acrobat is very slow, but still working, if Acrobat is actually frozen, obviously you won't be able to run a preflight fixup or save as an optimized pdf.