Outlook has no built in bulk attachment saver across messages, so the realistic options are a filtered manual pass, a macro or a tool. Which one depends on the message count.

Under a hundred messages: filter and grind. Search the folder for hasattachments:yes ext:pdf, then per message right click an attachment and Save All Attachments. Tedious but no setup.

Hundreds to thousands: a short VBA macro is the free answer. It loops the selected messages, checks each attachment name for .pdf and calls SaveAsFile into your target share. Press Alt+F11, paste a loop into ThisOutlookSession, select the messages and run. Add the received date to the saved filename inside the loop, invoices with identical names otherwise overwrite each other.

No macro policy or no appetite for VBA: attachment extractor tools do the same with a progress bar and filename patterns built in. Whichever route, do a ten message trial into a temp folder first and check the naming works before pointing anything at two years of mail.