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App to fill in and sign PDFs
(jlai.lu)
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
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I spent the day looking for a desktop app that does this and finally found Scribus. The fact that most desktop Linux PDF readers and editors cannot do this satisfactorily does not make me hopeful that such an app exists for Android.
PDFsam Enhanced may be what you're looking for…