Looking for Software to Scan or Convert to Searchable and Signable PDF
I know of a website that people have used that is supposed to be very good (there is no software to download) and everything is carried out online. It is called FillAnyPDF:

https://www.fillanypdf.com/default.aspx

which includes digital signature. I have never used it myself, but it may turn out to be what you are looking for, but it might just be for form filling.

Alternatively Wondershares PDF Editor for Mac maybe cheaper than Adobe:

http://www.wondershare.com/mac-pdf-editor/?icn=pem01&amp;ici=top_side

I left another suggestion in the comments below however this article by OSXDaily (particularly the comments section) should provide more insight to your needs:

http://osxdaily.com/2009/09/12/pdf-editors-for-mac-os-x-whats-the-best-way-to-edit-a-pdf-on-your-mac/