Hi Jayant,
Here are the steps to upload a file via the API:
1) Create a Document object using https://api.clarizen.com/V2.0/services/data/CreateAndRetrieve;
2) Create an AttachmentLink object between the project and the document created in step 1 using https://api.clarizen.com/V2.0/services/data/CreateAndRetrieve;
3) Perform GET on https://api.clarizen.com/V2.0/services/files/GetUploadUrl;
4) Perform POST of your file to the URL returned by step 3;
5) Perform POST on https://api.clarizen.com/V2.0/services/files/Upload with documentId(entityId) from step 1 and fileInformation parameters to attach the file to the project.
Hope this helps.
Roland