Answer
“Fillable form” and “Active XFA Form” PDF files, will not upload properly for use with DocuSign. To work around this difficulty, fill out the form in Adobe Acrobat and print it to a PDF file (can be chosen from the Print menu in Acrobat). Then, upload the “printed” file, which will work with no problems.
PDF files larger than 5MB are generally not safe for use with DocuSign. In Adobe Acrobat Pro, you can do a Save As and save the file as a Reduced Size PDF or as an Optimized PDF, both of which will allow you to reduce the file size.