It is a standard document with searchable texts and all operations are allowed (no security restrictions), but highlighting and all editing functions are disabled.
This is probably related to the following two cases:
A PDF/A compliant PDF file is opened in PDF/A view mode in Foxit PhantomPDF.
PDF file is opened under Protected View mode in Foxit PhantomPDF.
Solution for the first case
For the first case, document opened in PDF/A view mode is read-only. Most editing functions under this mode are disabled to prevent modifications on PDF file. To enable editing on PDF/A compliant file, you can complete it in the following ways:
When a PDF/A compliant document is opened, a bubble message appears at the top right corner of the document area shown as below. Click on Enable Editing, accept the change by clicking on Yes.
In some cases, the notification messages in Foxit PhantomPDF were set not to show PDF/A message again under General tab in Preferences window. There would not be any bubble message appearing even when a PDF/A compliant file is opened under PDF/A view mode. Then you should turn off PDF/A view mode via Preferences.
If you have a lot of PDF/A standardized documents to process routinely and want to improve your productivity, you can set up your application to never open PDF/A document in read-only mode, so that you can directly open and edit it.
In your application, go to File > Preferences > Documents, change View document in PDF/A mode to Never, click on OK to apply the change.
Solution for the second case
For the second case, PDF file opened under Protected view mode is read-only. Most functions are disabled under Protected View mode to help protect your computers from being harmed by files originated from potentially unsafe locations. The protected view feature is only available in V9.0.1 and greater versions. Before you highlight and edit on PDF document, you have to turn off the Protected View mode in bubble pop-up message or Preferences window. Follow this article to know how to turn off Protected View mode.