How to accurately reproduce PDF document scans using Acrobat Pro?

Current Process: I recieve hardcopy construction plans, sign them, scan them to PDF, and then re-transmit them electronically (lets call this a Final PDF). The process closely mirrors what was outlined in the post by OMN_G. (I however do not wish to use password protected files, as discussed below)

Desired Outcome/Final Product: I am trying to elecronically reproduce the process of scanning a signed, hardcopy plans to create a Final PDF that cannot be easily tampered with minimal distortion. (I believe this could be considered an "image" or rasterized PDF, but I am not up on all the industry specific PDF lingo).  

Issue: All of the options in Acrobat Pro I have investigated have not been able to provide both the security (preventing signature tampering) AND functionality (allowing signed PDF pages to be inserted into larger plan documents) that hardcopy scanning previously provided. *My test for security is to use AdobeAcrobatPro > Tools > Content Editing > Edit Text & Images and try to lift/manipulate/copy the electronic signature. This is the highest level of security desired. (Yes, I recognize that this process is not 100% "secure" and can be easily edited by a motivated Photoshop user.)  

Investigation: I have attempted multiple solutions within Adobe (electronic signatures, certified signatures, password prohibited editing, flattening). None provide the security* AND functionality of our current scanned documents. Using the Print function (Adobe PDF as the printer) after applying electronic signatures also proved easily editable when in the Advanced>Print to File configuration. Print>Advanced>Print to Image provided a result close to the original process, however the time to print/export is quite long and the resulting Final PDF image quality can be somewhat distorted (even after changing to different DPIs).  

More robust security* solutions (certified signatures and password protection) do not allow pages within the Final PDF to be combined into larger PDF plan documents. The functionality of being able to combine PDFs is necessary when sending Final PDF files to my clients. Electronic signatures are preffered over signing with certificate due to the ease of placement on multiple sheets within the document (without creating form fields and/or saving the document each time every sheet is signed, ad nauseam).    

Current Solution: The closest solution I have found has been to apply an electronic signature within Adobe, save the file, and then use Tools>Protection>Sanitize Document to "flatten (again might not be the correct term)" the document to secure* it. The process works great on recieved "dumb" PDF plans (that have been hardcopy signed & scanned), but experiences distortion & conversion issues on "smart" PDF plans (that have had a signature applied electronically and all the plan components/drawings maintained).    

Is there a process within Acrobat Pro that is able to replicate the process to produce a Final PDF (as described above)?