I have been trying to solve this issue for the last 2 years and I finally figured it out!
When calibrating my iMac I noticed that the Adobe RGB setting looked like the dull PDF's that I had been exporting from Vectorworks. When I changed the setting to Apple RGB the drawing inside of Vectorworks looked correct but when I exported the PDF again I had the same issue.
To fix the PDF color on export I had to:
1. Navigate to: /Library/Application Support/Adobe/Adobe Photoshop CC 2017/PDF
2. Click on High Quality Print.joboptions
3. Select the Color Tab
4. Click the Color Management Policies drop down menu and select convert all colors to sRBG.
5. In the Working Spaces below under the RGB dropdown select Apple RGB
6. Select okay and overwrite the existing profile.
Note you may have to do the same for the High Quality Print profile in this location:
/Library/Application Support/Adobe/Adobe PDF/Settings
