You can get project converted document id by project document revision Id from here
Query String
Parameter
Required
Value
docRevisionId
Mandatory
User Input
convFileType
Mandatory
User Input
Request Header
Parameter
Required
Value
TokenKey
Mandatory
User Input
PINProjectID
Mandatory
User Input
Request Body
Response
DocumentRevisionID:1234Cache-Control →no-cache
Connection →Close
Content-Length →5
Content-Type →application/json; charset=utf-8
Date →Fri, 27 Jan 2017 12:59:10 GMT
Expires →-1
Pragma →no-cache
Server →ASP.NET Development Server/11.0.0.0
X-AspNet-Version →4.0.30319