Some possible approaches -
Acrobat Pro supports "edits" to PDF page content. Awkward (as PDF is *not* a word processor file format) but doable. One file at a time.
Export the PDF content to Word (assumes straight up textual content) then do edits - then create fresh PDFs if needed.
I guess I should have explained more clearly. This is my first time using a forum. The text I am attempting to replace is within an interactive block or fallible block in the PDF documents. I've found multiple 3rd party software that will search and replace text within the 400 PDF documents successfully but so far none of them can replace text located in an interactive block. Example: Top left of each document contains a date as such;
The underlined portion is interactive and each of the documents currently has a date of 06 Oct 2016. I would like to search for 06 Oct 16 on all 400 documents and replace it with 02 Feb 2017 rather than opening each document and modifying them one at a time. This is something I will need to do on a regular basis and the first time I did it I spent 5 minutes on each document (had to change more than just the date) so about a weeks work just updating documents.
Which exact version of Acrobat do you have?
Do all of these fields have the same name in all of your files? If not, do you want to search all the (text) fields in the field and if they have a specific value ("06 Oct 2016"), replace it with the new value ("02 Feb 2017")?
I've developed a tool that does that for you and it can even be used in batch process (aka Action) on multiple files, but it only does one field at a time. It will not be too difficult to customize it to your specific needs so that it performs multiple such search&replace commands in one process. You can find it here: Custom-made Adobe Scripts: Acrobat -- Search & Replace Text in Form Fields