Converting Microsoft Word forms into InDesign documents

I can't conceive of what 1900 forms are for, but I guess that's irrelevant.

The problem here is the immense sunk costs in Word, which should have been abandoned for either a dedicated form manager or at least a more sophisticated tool like ID long ago. But that's irrelevant as well, I guess.

The only advantage to pivoting to InDesign is that it's a more capable tool, and would allow things like linking logos, signature images, addressing blocks  etc. to help speed both individual form and more global changes. It also integrates with/exports to Acrobat much better. But there's no particularly short and straight path from a Word form to an InDesign form, even if scrupulously rigid processes and formatting were used in all 1900 iterations. (My guess: a shortcut or two crept in.)

The suggestion to use Acrobat to its full capabilities and edit/modify PDFs is probably your best path. But that of course leaves you with largely fixed forms until and if you start converting them, or keep managing them in Word and exporting to new PDFs, hopefully with the updated elements.

If it were my circus, I'd look into the specific form creator/manager tools. I know they exist, and exist in part for situations just like this.

I'm not going to venture an opinion about the logic of converting 1900 Word docs to InDesign, however, there is an Acrobat tool that may help, the "Replace Pages" tool will take the content from one pdf document (from your revised Word file) and replace the content in the target pdf, all form fields will remain unchanged. Also, form fields can be edited in Acrobat.

If they are PDF forms and all you need to change is the artwork you can do so in Acrobat fairly easily. I can't imagine this project being worth the time and effort to convert to InDesign but if there's more details you can share we can help you out with a decision.