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Allow the user to control content the text size on mobile devices with small screens.
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Unlike web pages, PDF documents are not responsive and do not adjust to your screen size, such as on a mobile device. This forces the user to have to zoom in and the swipe left to right /right to left in order to read the content.
8. Allow Keyboard Control for Touchscreen Devices
Allow mobile devices to be operated by external physical keyboards or alternative on-screen keyboards.
WCAG Mobile Related Guidelines
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