Add text layer to all files in folder: what about files that already are searchable?

Question

Hi everyone
I'd like to make my scanned PDF documents searchable using the OCR feature of Adobe Acrobat X Standard. The scanned PDF files are stored in one folder (or its subfolders respectively). In principle I could just go to the OCR feature, tell it to add that folder to the OCR conversion list and replace all PDF files in it with searchable versions.
Some of the files in the folder, however, already are searchable because they were created from Word files for instance. My question is: What will Acrobat's OCR feature do with these files that already are searchable? Will it leave them unchangend? Or will it create new files and replace their existing "text layer" with a new text layer?
One of the reasons for my question is, that the existing "text layer" is free of recognition errors by definition (because it has been added by Word's conversion feature). This means, a new text layer added by Acrobat's OCR feature can only be equal or inferior in quality compared to the existing one. In the latter case, it wouldn't make sense to replace the existing "text layer".
A second reason is that some of the already searchable files have security properties (i. e. signatures). What is going to happen to them when the OCR feature creates a new file?
Thank you for your answers!

Answer 1

The usual thing is that Acrobat will object, saying the file contains "renderable text", and do nothing.
OCR on a file with signatures will, at best, invalidate the signature. More likely, all trace of the signature will be deleted, and it will attempt to do OCR on the visual appearance, finally leaving a graphic. OCR is  not really intended as a late-stage process.