PDF export preset color conversion

Yes all of the document color—images and native process colors in a color space that conflicts with the Destination—would get converted into the chosen Destination profile.

There are some things to watchout for: the Conversion Options (Intent and Black Point Compensation) used for the conversion come from the current Color Settings Conversion options, unless you have overridden the options in Edit>Assign Profiles, or Object>Image Color Settings. Also, unless there is a specific reason, the Destination should be Document CMYK rather than Working CMYK. The document could have a CMYK profile assignment that is different than the Color Settings’ Working CMYK—if there is a conflict, Black only text would get converted to 4-color CMYK.