When viewing a PDF from AutoCAD in a Foxit Reader, frames are displayed around texts.
The frames displayed around texts are comments in PDF file, it indicates that those texts contain associated comments.
On the command line in AutoCAD, enter EPDFSHX and change the value to 0 (zero). In AutoCAD 2017, the command PDFSHX maps to EPDFSHX (either may be typed in). For AutoCAD 2016, the core AutoCAD 2016 Service Pack 1 must be installed in order to have the EPDFSHX variable (see Autodesk Downloads).
NOTE FOR DWG TRUEVIEW: As there is no service pack for DWG TrueView 2016 to add the option of disabling the feature, there is no way to prevent SHX text in a DWG from becoming comments in the resultant PDF when creating PDFs with the built-in PDF driver. For DWG TrueView 2017 and newer though, the variable is part of the program, but it can only be modified by editing the Windows registry. If you are unfamiliar with the Windows registry, please contact your IT professional for assistance, as improperly editing the Windows registry could render your computer operating system unusable.
Follow these steps to prevent DWG TrueView (version 2017 and newer) from converting SHX text in a DWG to comments in a PDF:
Press WINDOWS-R on the keyboard to bring up the Run window, enter REGEDIT and click OK.
Navigate to the following key:
(The 'x' represents characters which vary from version to version.)
Change the '(Default)' value from 1 to 0.
Problems caused by improperly editing the Windows registry could render your computer operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft Knowledge Base. Use the Microsoft Registry Editor only at your own risk and only after backing up the registry as outlined for your operating system in the Microsoft article How to back up and restore the registry in Windows and in the related solution How to backup the system registry. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.
The original source of the above mentioned solution comes from this article in AutoCAD knowledge center.