There are many business cases where this would apply so I will just share a little information on this one. I was not able to find a filter by sales order of job no. when calculating the plan for the requisition worksheet. It would be interesting to know the effort required to customize the filter to include an option for a SO or JOB#.
A purchase order can be created directly from a sales order via the command bar > More options > actions > Functions > Create Purchase Document. Hopefully the group can share some additional tools that can be used when buying for jobs.