I have been noticing that over the past few weeks that I am being contacted by users of DocuSign because of The Validation of the PDF file Failed message. It seems that DocuSign is able to read the PDF file correctly but is not able to make any changes (such as adding a signature) due to the PDF files having a password being enabled thus protecting the file from being edited.
The best solution that I have found is to remove the password, resave the PDF files, then upload to DocuSign. If you do not remember the password or had set the password, some websites offer the service of looking up or removing passwords from PDF files but I do not recommend such services as other entities will have access to your documents. I recommend recreating the document from an unprotected template and then upload it to DocuSign.
For some reason or another, the color or type of font can cause the failed message to appear. My solution to you is to try and select different or universal font that will have more success or change the color if that applies to your documents.