How to create automatic customer Invoice

Hi,

I am working as a end user in MNC company. In a month i have to post approx 40 customer invoices in SAP.

first i have to create Sales order in VA01 and then final invoice in VF01 and take PDF copy and save to drive.

I have to post invoices in different contract with different line item and WBS.

Ex. suppose i have to post invoice in ABS contract so in that contract 100 line item and each line item different WBS.

now today i have to post invoice on line 20 and 40 and next day posted on other line item.

I had record the script and run but the problem is every time i have to record separate script because every time my line item is changing and contract.

Can anyone help how to automate this activity.

Thanks,

Rahul