[CentOS] digital signature equipment

Everyone,

I apologize if this is off topic for this list!!!!!

I have an application that I need to acquire, store and merge to a pdf file a digital
signature from a client.   What favorite equipment do some of you use to do this.

I contacted the topaz systems support team, and they advised me their equipment produced a
proprietary file type, and required me to sign a non-disclosure agreement to do what I was
asking to do.  I indicated I was willing to proceed, but I have not been able to get them
to communicate in follow up. .... probably related to the holidays.

I will be using Centos 7.5 Desktop units to acquire the images and send the images to a
Centos 7.5 server that will do the storage, and merging work.  I have been able to use
pdftk to merge previously obtained signatures, but I have not been able to find a piece of
equipment that I can use to acquire signatures on the fly and merge them easily to a pdf
form file.  

Any suggestions would be appreciated!!!!

Greg Ennis