Documents received through WhatsApp or email can typically only be saved to the device under compatible apps or within the Files app, which is the default file management system on iOS. This means that if you receive a document via WhatsApp or email, it cannot be directly stored in arbitrary locations on your phone. Instead, it has to be saved within apps that are designed to handle the specific file type (e.g., a PDF reader for PDFs, a Word document viewer for DOCX files) or placed within the Files app where the document can be organized into folders.
For WhatsApp, documents can be saved to either the app’s local storage or to the Files app, depending on the file type and your storage preferences. Similarly, emails often allow you to save attachments to the Files app or an app associated with the file type (like a PDF reader for PDFs or a note-taking app for text files).
By default, iOS doesn't let you save these documents to random locations outside of supported apps, which is a measure to maintain organization and security on the device. However, you can move files within the Files app itself, organizing them into folders or sharing them with other apps.