Payslip Import must be enabled. This is done under:
Company -> Advanced Settings -> Payslip Import
If you enable this setting, you will be able to import employee payslips into Salary. This can be done under the "Employees" tab by clicking the "Import Employees" button. Under Employees, you can now select Import Employees.
Select format and click "Continue to upload".
Upload the PDF file containing the payslips on this page. You can then proceed to view the data afterwards.
[!IMPORTANT] You can only upload one PDF file at a time, so please combine all payslips into a single file before uploading.
After this is done the starting balances needs to be controlled.
You can see here how it is done: https://help.salary.dk/en/articles/11582639-setting-up-start-balances