Exporting a space has a "exportAll" parameter String exportSpace(String token, String spaceKey, String exportType, boolean exportAll)
However, there is no equivalent exportAll parameter on the PDF export API - https://developer.atlassian.com/display/CONFDEV/Remote+API+Specification+for+PDF+Export

This may result in a different behaviour to exporting the space to PDF via UI - need verification
^ UI and Soap both hit the same service in backend. There is no concept of an "exportAll" parameter - the entire space is always exported to PDF