"To preserve appearance some text has been outlined"
I recently sent a PDF file generated from InDesign (CC2018) to a book manufacturer from which they were to make a brass die to stamp a binding, just as I have done for about twenty years. A proof was sent back to me in which the 1/2pt rules had thickened to about 3pts and some of the type had thickened, too. I complained and they sent me another proof, in which the rules were ok, but most of the type had thickened.
I wondered how this could have happened, so I did some experiments. I opened the PDF in Illustrator (CC2018), thinking they might be turning the art into outlines. In Illustrator, the file opened with a dialog box "To preserve appearance some text has been outlined," which offered no way to opt out. Sure enough, the artwork (type and rules) had thickened as it did in the proofs.
Why does Illustrator do this? It doesn't preserve the appearance of anything, it only ruins the art. This is clearly a glitch. To fix it, I had to edit the file extensively. In the least, there should be a way to opt out of this "feature."
PDF is intended for Output and Document Sharing. In any workflow, if the content is to be modified without any data loss then the native file format should be used for editing. InDesign document or Illustrator document should be used to edit the content.
I have had this issue MANY times, while working on restaurant menus....not fun! ADOBE, please address this issue with text being outlined!
Scott, I have been struggling with this issue for many years with no simple end-all solution. One process which only works less than half the time is to place the PDF into a blank InDesign page/document, and then re-export to PDF using PDF Font inclusions settings set to “include all fonts”. The newly recreated PDF will allow you to open, possibly open with missing font replacement dialog, or just fail and outline 1/3 of the charecters again. Hope this helps