You can easily consume item/resource/expense on the Maintenance Work Order directly from the Purchase Order.
When you creating the Purchase Order - you can decide for which Work Order this record should be applied or even choose existing line that fits to the record you are about to post.
On given example, where we have two work orders.
One has already lines for resource/item/expense the second one is totally empty.
On the purchase order we defined that some lines must be applied to the work order with lines (the Work Order Line No. is defined), and some lines must be created (when the Work Order Line No. is not defined - the new line will be created). All fields on the Purchase Order Lines are hidden by default.
The Work Order Line Type is defined - without that lines will not be applied to the line.
You can only apply consumption on the items and resources that are defined as Maintenance. When you want to apply consumption to expenses - you must use G/L Account No. that is defined on the Expense.
When you post the Purchase Order:
You can also create a Purchase Quote where you can define all values that you can find on the Purchase Order (related Work Order) but also Work Order Plan - or even only this value. Work Order Plan No. later will be added to the line on the Purchase Order and you will not be able to post the Purchase Order until the Work Order No. is blank. This is because someone by purpose decided that Purchase Quote is related to the Work Order Plan.