Youy must not connect databases : direct uypdates in DB will set the mess.
You will quick have unconsistencies.
You must use features provides by ProjeQtOr : API or Import.

Is there a way to do this automatically?

API calls must be done from other application.
So automation must be done on that side.

Import can be automated on ProjeQtOr side : in global parameter, define automatic import location.
File that a stored here will be imported.
But once again, other application must push there files to be imported.

There is no "magic" automation.

So if I follow you correctly, in the folder defined for import, if the source application generates a CSV file usable (field names) by ProjeQtor, including only the new cases to be processed (to avoid duplicates), ProjeQtor will automatically process this file each time it is in the folder. Do you have to delete the file from the import folder after each processing?

So if I follow you correctly, in the folder defined for import, if the source application generates a CSV file usable (field names) by ProjeQtor, including only the new cases to be processed (to avoid duplicates), ProjeQtor will automatically process this file each time it is in the folder.

Yes, exaclty.
You can also update items if you provide the projeqtor ID (the other application need to know this id for that)

Do you have to delete the file from the import folder after each processing?

No, this is automatic.
File is automatically moved to sub-foler "done" (or error if treatment failed)

I don't see where to set the local path of the folder for the automatic import files?

On GLobal Parameters / Tab "Automation"
 

there is no field directory: