You could create a workflow which monitors to see if a document with this template is created, and then adds the PO Number field using "Assign Field Values."

There isn't anyway currently to have a template field which selectively shows information based on whether you are creating the template or filling in information. Also there isn't a way to change template security through workflow, so you couldn't make the field hidden from all users until creation either.

How is it be kept hidden on the template? Can you please show me a screenshot of what u explained.

I believe that the only way to keep it "hidden" would be to NOT have it included as part of the template at all.  Through the Workflow, you would add the PO field to all documents of that type.  Using Kevin's solution, the Workflow would add the field to that particular document, outside of the assigned template, with a null or 0 value, then the PO field would be available on the document.

On the Assign Field Values task, you would "Keep the current template".  When choosing the fields to add, you would not select a template from the drop down and select the PO field to be added to the individual document which the Workflow is processing.

Thanks for your reply.

Is there no other solution apart from WF? But, if the field is attached to the template, it will not be possible to hide / show other fields accordingly.

Please reply

Someone from Laserfiche please correct me if I am wrong, but I don't believe so.  The only possibility I can think of would be to add a security tag that would make the field unavailable to all users, then in the workflow, after the needed metadata is completed, have a workflow action that removed the tag, but I do not believe tags can be used in this manner either.

Tags don't work on fields, although that's an interesting idea. 

As Kevin and Glenn have noted, there's no way to make a field selectively visible in a template. A field is visible to a user across the entire repository, so you'd basically be setting that a user could see it in ALL instances. The approach of having workflow add it independently is the best if you want it to not be present/invisible to users at creation time - there's no direct way to do 'show this field based on the value of another field'.