Some companies want resumes submitted as text or .DOC, for easier keyword searching perhaps. Or to avoid viruses? So the recruiter may OCR the PDF, then "improve" on it.
It's really not made to be and with the exception of an embedded file that's actually editable (eg: LibreOffice optionally keeping an ODT version inside the PDF), "editing" a PDF tends to be a disaster of trying to match the layout with whatever text you are attempting to edit.
Certain tools, such as Word and LibreOffice, make it a bit easier as most of the source text is in the document, others like LaTeX end up looking like garbage through machine processing.