Looking for an Adobe Acrobat alternative (PDF-editor)

I'm looking for an Adobe Acrobat alternative, or PDF-editor, that is capable of:

• marking text;
• adding text;
• adding comments (like one would do in MS Word);
• adding a signature (in some way);
• preferably, but not necessary: the ability to recognise text in files where the text is not selectable (i.e. one can copy text from an image file that was saved as a PDF, like some printers do when scanning pages).

Does anyone happen to know of any European or Open Source alternative that fit this description? I have sworn to never again install any Adobe software.