A way of restricting users to only specific documents is by adding "User Permissions".
User Permissions can be used to restrict access to select documents based on the link fields in the document. For example, you can select specific Projects, Sales Order, Purchase Order that can only be accessed by a certain user. Although he has access to these Document Types, the only Projects, Sales Order, Purchase Order that will be displayed on his account are those added on User Permissions.
To create User Permissions:
Login to ERPNext. Go to Users and Permissions.
Select User Permissions list, click on New.
Select the user for which the rule has to be applied.
Select the type of document to be allowed (for example "Project").
Under For Value, select the specific item that you want to allow (the name of the "Project").
If you check 'Is Default', the value selected in 'For Value' will be used as default for any future transactions by this user.
7. Click Save to Apply the Changes.
8. In this example, the user will only able to see the "Special Blend Arabica" on Project.