Hello,
My name is Andrey and I have some expirience in this area (Google Script and JavaScript). That's why I believe that I can solve this taks for you.
However it will be nice, if you can provide more details about your workflow. From description I understand that:
a) some person Mr. A create Google Doc with purchase order (PO).
Q: Is it a pdf doc or normal Google doc?
b) details of this PO should be placed in the Google sheet.
Q: Is it should be done in the scope of this project?
c) another person Mr. B should approve this PO.
Q: Mr.B should be notified about new PO? How?
Q: Mr.B uses Google Form to approve this. Is it correct?
d1) In case if PO was receted:
Q: Mr. A should be notified about that via email. Is it correct?
d2) In case if POS was approved:
Q: Email to Mr. A and and bookkeper Mr. C should be sent? Is it correct?
Having these information I'll be able to provide more detailed estimate.
If you wish we can discuss this project via chat/skype.
Thanks,
Andrey.