Zoho Writer and Zoho Sign - Size Limit!?

Hi,

I am developing a CRM mail merge template which we will be sending to clients to authorise using Zoho Sign. It is a big template. I can merge to a new document fine, but when merging for sign collection, it fails with:

There was a problem initiating sign collection. Please try again in a while.

and when I look at the log it shows:

Failed to send the document for Sign Collection. File size exceeds the maximum limit

How can I:

Increase the size limit
See what the size limit is
See what size the file/template is currently

Thanks.