I have encountered an issue in Adobe Acrobat for iPad (3rd Generation, Version 16.12.15 ). The example is a PDF I created from the program MuseScore. The first image is the initial page as it is opened in the app, with the toolbar at the top. The second image is when I tap the document to open to full screen. The contrast changes and I lose sight of the music lines, making it impossible to accurately read. I do not encounter this issue with scanned PDF images, only these exported files from MuseScore. I do not encounter this issue in iBooks. Any help road ice would be appreciated, thanks.
Without seeing the actual PDF files, it's impossible to say what's going on, but this looks like a bug in how the application displays thin lines. In the desktop version of the application, you have control over some of the rendering:
As you can see, there is an "Enhance thin lines" option, which makes sure that thin lines are always rendered correctly. There is nothing comparable available in the mobile version of Reader. You may want to file a bug report: Feature Request/Bug Report Form