Hello Saichandana!
All these scenarios are possible to automate with the right people and technology involved. It's important to note that implementing this automation will require a good understanding of how SAP works and connecting with someone who knows SAP Basis may be helpful.
Below is a high level overview how this could work:
1. You can use AIBuilder to consume PDFs to pull information out such as PO numbers, transaction codes, customer information, etc. This is required if you want to use information in the PDF as part of the process. I'd highly recommend that those PDFs are standardized as well to improve accuracy.
2. Then use Power Automate to transfer that information to SAP to create the appropriate items in SAP so you can have approvers go in and acknowledge. You can upload the PDF itself as well if that is needed to help with the approval process.
3. You can use PowerApps as a portal for approvers. Where they pull all required approvals can be in one place.
4. Then on approval, or rejection you can have separate Power Automate flows to to create invoices or send to the next level.
Hope this helps!