When referencing a PDF report using APA style, should I cite the authors or the organisations?

If the report doesn't explicitly identify individual authors, attribute the most precise organisation/group responsible for the report as the author in your reference. The parent organisation's name should be included in the reference as the publisher. Organisations named as authors do not need to be repeated in the publisher information.

Example: 

Palliative Care Outcomes Collaboration & Australian Health Services Research Institute (2020). Assessment & responsible protocol. University of Wollongong. https://documents.uow.edu.au/content/groups/public/@web/@chsd/@pcoc/documents/doc/uow275153.pdf

The  above report doesn't clearly mention specific authors instead it states the document is prepared by Clapham S, Connolly J and Hope C . Both the Palliative Care Outcomes Collaboration and the Australian Health Services Research Institute,  affiliated with the University of Wollongong, are the group authors for this resource. The intellectual property belongs to Palliative Care Outcomes Collaboration, University of Wollongong. According to APA rules when a number of organisations/groups are listed as the author, use the most specific organisation/group responsible for the report as the author in the reference. 

In this case the group authors would be: Palliative Care Outcomes Collaboration & Australian Health Services Research Institute

The name of the main organisation appears in the reference as the publisher.

In this case the parent organisation or the publisher would be University of Wollongong.

To create the reference for an online document with multiple group authors, follow this structure:

Organisation/Group A & Organisation/Group B. (Date). Title in italics. Publisher. URL

Have a look at the APA Guide example for multiple group authors