Phone PDF AppsAdobe Acrobat ReaderAndroid & iOSThe most widely used, reliable, free PDF viewer and editor.Features include opening PDFs, adding comments, and signing.
Google PDF ViewerAndroid (usually pre-installed on stock Android devices)Fast and simple PDF viewer, uses little space.
Xodo PDF Reader & EditorAndroid & iOSFree, advanced PDF reading and editing features.Supports synchronization and cloud storage.
Foxit PDF Reader MobileAndroid & iOSLightweight, fast, and secure PDF reader.Includes note-taking and form-filling features.
WPS OfficeAndroid & iOSA powerful PDF viewer and editor included in an office suite.
Computer PDF AppsAdobe Acrobat Reader DCWindows & macOSThe most comprehensive and popular PDF viewer with commenting and editing tools.The free basic version is very powerful.
Foxit ReaderWindows & macOS & LinuxLightweight, fast, and easy to use PDF reader.Paid version available with advanced features.
Sumatra PDFWindowsVery lightweight, fast, and simple PDF viewer.Ideal for basic viewing only.
PDF-XChange EditorWindowsFeature-rich, free and paid versions available.Great for editing and annotations.
Google Chrome / Microsoft EdgeWindows & macOSModern browsers can open PDF files directly and provide basic reading features.

Summary

Platform
Program Suggestion
Features

Phone
Adobe Acrobat Reader

Reliable, feature-rich

Phone
Xodo
Free, supports editing

Computer
Adobe Acrobat Reader DC
Professional, popular

Computer
Foxit Reader
Lightweight, fast

Computer
Sumatra PDF
Very lightweight, simple