I would use the ITPilot Wrapper Generation Tool to retrieve a PDF from a REST API:
* Record a navigation sequence for the specified REST API URL to download the PDF file.
* After the file is saved to disk, stop the recording and import it into the Sequence component.
* Deploy the created Wrapper to Virtual DataPort along with "Create base view" option checked.
To schedule this process, I would use Scheduler Administration tool and schedule a job of type VDP that points to ITPilot base view created in the previous step.
For further information, you can have a look at the [Downloading files and images](https://community.denodo.com/tutorials/browse/webautomation/2patterns-g) section of Tutorials and [Time based Scheduling](https://community.denodo.com/docs/html/browse/6.0/scheduler/administration/creating_and_scheduling_jobs/configuring_new_jobs/time-based_job_scheduling_section) section of Scheduler Administration Guide.
Hope this helps!