This App "PDF Utilities" comes to rescue. With this you can easily unlock the PDF without much effort, so that changes can be made.
Another handy feature is remove pages from a PDF for simpler printing. You must not specify, which pages should be printed to exclude some pages (which is often very tedious).
A new feature is adding of blank pages in an existing PDF file. This is convenient for additional notes, if the space on a page is not enough.
Another Feature is automated removing of blank PDF pages.
And all this without sending the PDF file to a webservice, it remains on the device.
The app supports Dropbox, now. PDF-Files can be selected and processed directly out of the Cloud.
• Remove the write protection of a PDF file (without knowing the password) –> PDF Unlock
• Removing encryption from a PDF file (the password must be known, because the file is encrypted)
• Remove selected pages of a PDF file
• Add blank pages to a PDF file
• Automated removing of blank PDF pages
IMPORTANT: Because of limitations of writing on external storage, which was introduced in Android 4.4 (affects mainly the Samsung Galaxy devices), it is currently not possible to process PDF files from external SD cards. When a workaround exists, this is implemented in one of the next versions. Please copy the PDF files to the internal memory before processing.
The FAQ can be found here: http://www.mdev-germany.de/android-pdf-utilities-english#faq
** If you have problems when using the app, please drop me an e-mail to firstname.lastname@example.org and try fixing this problem with me. Please do not write a bad rating immediately.
Thank you. **
Updated for Android 8.0.