Thanks for your interest in our products.
I tested the scenario using Aspos.Pdf for .NET v6.8 and unable to notice any problem in size using stream or file. During my testing I generated two files, one using file attachment and second using stream attachment. Both files are same in size and attached for your reference. We would appreciate if you try to use the latest version and check if it fits your need.
Please feel free to contact support in case you need any further assistance.
Thanks & Regards,