So I tried many ways to save out text which was knocked out within a shape and I found two beneficial solutions.
1. File > Export > Save > Select PDF/X-1a:2001, under the Adobe PDF preset menu. This should now export the document with the knockout text/object showing.
2. Alternatively, you can save out the pages required as a Jpg image and then use www.smallpdf.com to convert the jpg to a pdf. You can then attach that one page to the rest of your pdf document if need be, using the same third party website provided.
I am having the same issue, but the pdf I am trying to export is supposed to be interactive with hyperlinks. So if I flatten the pdf to a jpg the interactive part won't work anymore... Any suggestions?? Thanks!
Please tell us exactly what you're trying to do along with InDesign version, operating system and version of Reader or Acrobat.