With respect to the above question follow the below steps to get those options in page layout.
• Login to your salesforce account
• Click on set up
• On the left hand side click on the customize in that select opportunities
• In the opportunities you can see the record types click on that after that click on the record type name
• There you can see the generate field click on that select Invoice, Salesorder, Estimate, add them and save it. You will get the Options in the Generate filed.
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