CorelDraw graphics editor has known issues when importing PDF document files not exported by CorelDraw itself.
Even slight oddities in the .pdf file can cause CorelDraw to not recognize any data. This is typically the case for older PDF documents which, when imported, cause "File is corrupted" error window.
It was reported to us that a quick fix for this would be to simply re-save your .pdf again (PDF/A or PDF/X) using latest Adobe Acrobat Reader. So this may be one of the first thing you can try to "fix" .pdf documents so they can be opened in CorelDraw.
Even better solution would be to re-save it as one of the PostScript files (.ps, .eps) that can be imported to CorelDraw without any trouble. With a valid PDF/PS document you should now be able to import it to CorelDraw and pick to import curves or texts.
Of course, for pdf to cdr conversion to work, you need CorelDraw. Unfortunately, we haven't found any 3rd party utility that could directly and reliably convert pdf to cdr files.
Mac users have even less options, because CorelDraw is not available for MacOS, so you would have to launch it in Windows virtual machine.