I know that PDF Studio supports AES 128 and 256 but if you're sharing a secure document then you really need to make sure that you use the more modern encryption. Whichever PDF reader you choose if security is important then make sure it supports AES as many (on Linux) only still support RC4. Personally I like the PDF/A functionality (long term PDF archive) because you can be fairly sure your document will be readable in 20 years time. There's also the option of ensuring that your PDF complies with the relevant standards using their inbuilt validation tool as I'm often sharing documents with people who have older PDF reader installed. Of course you can disable that if necessary although for me that's the killer feature. Unlike a lot of the other software I've tried (on Linux) PDF Studio has proper OCR integration so that you can create a machine searchable PDF.

LibreOffice doesn't allow you to do this in many cases and distorts your PDF.

PDF Studio has granular control over the layout of your document and you can create a new PDF from scratch or import an existing one. It has all the normal functionality including the ability to make/edit PDF's, create/complete forms, encryption/protection, digitally sign, watermark, OCR, editable text, redaction, optimisation, convert to raster, redaction, linearize, convert to HTML5/SVG, bookmarks etc. It's continually maintained and updated and is cross platform (Mac, Windows and Linux). My personal recommendation would be PDF Studio.

Most are no longer in active development, have a poor GUI or don't have the functionality I require. There's plenty of free, open source software for Linux Mint but as a user of the platform myself I can't say that I've been particularly impressed by any of them.

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