PDF Expert for iOS lets you color code files and folders to organize them more effectively. Here’s how to add a color tag:

1. Launch PDF Expert.
2. Tap  More … on a file or folder.
3. Select Mark With Color Tag.
4. Pick a color.

How to add color tags to multiple files at once:

1. Tap ... at the top right > Select  .
2. Choose the needed files or folders.
3. On iPad, tap Mark With Color Tag on the sidebar.
   On iPhone, tap More at the bottom and select Mark With Color Tag.

As for the Mac version of the app, you can easily add tags to your PDFs in the Finder app.