Reports can be created from the PO module as well as from the Incoming Invoices module.
For printing multiple Reports, select (highlight in yellow) the Purchase Orders or Incoming Invoices that you wish to include and click on the Reports icon at the bottom of the window, or click on the drop-down arrow on the top left corner and select Reports.
To print a Report for a single PO or Incoming Invoice, open it and click on the Reports icon at the bottom of the window.
For more complex reports, use the Financial Reports where you can select a specific Project and show details from all Purchase Orders created for outsourced services or purchased items for that project only, like buy price and supplier. And you can also follow up on the Incoming Invoice received, when it is due, if it has been paid, etc.
If using Budgeting module, you can use grouping 'Budget Detail', where all detail from Purchase Order and from Incoming Invoice are available for designing a complete report, even custom fields. These details have also been added to the 'Rows' section, in case you do not use Budgeting module.
For more details please refer to the Financial Reports articles.