Start with the formats you use
A useful Android document viewer should support the formats you receive most often. For everyday work, that commonly includes PDF, DOCX, XLSX, PPTX, JPG, and PNG.
Keep finding and viewing together
Switching between a file browser and several viewers adds friction. A file manager with search, sorting, favorites, recents, and an integrated viewer makes it easier to find a document and open it in one flow.
Understand cloud permissions
If an app connects to a cloud provider, check whether it can change files. Fileio uses read-only cloud access: Pro users can browse and open supported Google Drive and Dropbox files, but Fileio cannot upload or modify them.