It does not appear that Zoho Sign 'flattens' the PDF to embed the signature image into documents as post-signing it is possible to remove the signature image and re-save the file. This is a huge red-flag. DocuSign embeds their signature image into the document (I assume it is being 'flattened' upon PDF creation after signing) so there is no way to easily remove the signature. 

This was tested in both Apple Preview, and PDF viewer built into Chrome. It appears the signatures are showing as "annotations" and why it's easy to just select and delete.

With as much as Zoho takes security into consideration I am 100% surprised that this is a thing! Screen recording attached to show signature and initial fields being deletable from a Zoho Sign Document post-signing completed.