Updating PDF in Approval Center WF

Question

Our company relies on an approval workflow which is a serial approval allowing assigned people to markup/edit or simply provide feedback.

Currently we are using “Approval Center” for circulation. Things work great with Office docs, mostly Word. But with pdfs, the only way to mark them up is to download them, mark/edit and then reupload. The problem is that when changes are made to a document (possibly specifically on a Mac platform, then re-uploaded to the server) the chain of communication breaks. Thus downstream approvers are not able to convey their comments, or approval, because Approval Center regarded the updated file as new.

Our developer said that “Approval Center” has some updates to fix this, but is quite expensive. So they are suggesting another solution: to migrate our workflows into “Workflows List” (a Sharepoint feature) that allows us to keep workflows within Sharepoint environment.

The cost of making this change is expensive - about 40-50 hours of work and I am wondering if anyone has any other suggestions or workarounds. Thanks so much in advance!