Issue
When creating a Visualforce page from a Custom Object, the following error occurs:
[CustomObjectName] does not exist
Resolution
Append "__c" to the end of the custom object.
Sample code:
<apex:page standardController="Location__c"action="/apex/loop__looplus?sessionId={!$Api.Session_ID}&eid={!Location__c.Id}"></apex:page>
For more information, see Create a button to generate documents in Salesforce Lightning.