Scenario: if my company has different salesman and I want them to only be able to view their own created invoice or quotation.

Recently we have introduced a new attribute for each document, namely Owner. Every document (i.e. invoice, quotation, etc.) that is created from now on can set a Owner for it, or it will automatically set to the current logged in user if leave blank.

If you have set not to share the documents among every users, they will only be able to view their own documents, except they have the Admin role or User Sharing is enabled. This can be configured under My Biztory > User > User Sharing. 

If you want to further customize to each user, you may also override this global settings and configure at user level by editing each User > Sharing View to yes or no.