PDF Viewer uses the standard iOS document browser from Apple’s Files app. This shows files and folders, including local files, those in iCloud Drive, and those in third-party storage providers such as Dropbox, OneDrive, Google Drive or Box.
Apple’s secure and private design means PDF Viewer is only able to read and modify files that you choose to open. PDF Viewer can only change the color scheme and add buttons to the existing Files interface from Apple. We do not have control over other details, and unfortunately are unable to help with specific file transfer issues.
If you experience issues with file syncing, problems with downloading or uploading files, a good first step is to force the iOS document browser to reload by restarting your device. If this does not help, please reach out to your cloud storage provider and ask for support:
Google Drive: https://productforums.google.com/forum/#!forum/drive
If you are experiencing these problems with a particular file provider, another option is to copy or move your files to “On My iPad”, “On My iPhone” or iCloud Drive. You can temporarily copy the files into local storage or iCloud Drive while you are working on them, and then export them back to your preferred cloud storage provided when you have finish editing, like so:
In the Document Browser view, long-press on the document.
A menu will appear. Tap on "Move" in the menu.
Now select either “On My iPad/iPhone” or “iCloud Drive” and choose a folder.
Tap on “Move” to move the document to the new destination.