Fill and Sign form erroring as "not a valid PDF document" on android tablet in Reader

Can you please clarify a few things for us so that we can try to understand more about where the problem is occurring:

"I created a form with a signature field," - Can you please tell me what application (including version) and device you are using to create the form? This sounds like Acrobat Desktop, but I want to be sure.

" sent it to my android tablet and was able to sign it and send it back. " - What app are you using to sign it? Is this the Adobe Acrobat for Android? We don't support signature fields for forms in our Android Adobe Acrobat product, though we support signing using an annotation-based signature tool. Can you please clarify how you are signing?

"I added some calculated fields and while everything appears fine on the PC," - Were these added using the Acrobat desktop product? I'm guessing yes, but I want to be sure.

"when I send it for signature it now errors that the file is "not a valid PDF document" when the Reader tries to open it on the tablet." - Are you using the "Send for signature" feature of the Acrobat desktop product? If so, can you please confirm the version? Is it the same that you used to create the PDF?

It's hard to say what limitations you might encounter without knowing for sure what you are trying to do. I apologize for so many questions, but there are so many different possibilities with each step (between devices and applications and their different versions) that I don't want to speculate what may be happening without knowing more. Additionally, if you could possibly send me a sample file at I would appreciate it! Please send me a private message on the forum and I will give you my email address. Thank you for your patience!