PDF, the file format/technology, is not supportive of "editing" as is done in a word processing file format.
This becomes clear as you digest just what PDF is (as described in ISO 32000-1),
Using contemporary Acrobat / Adobe Reader you can make effective use of "shared reviews" of a PDF.
For "hands in the file" editing you must all use the same authoring application on the same authoring file in an environment that provides firm version control.
Be well...