Can I convert only part of my RRSP to a RRIF and keep the rest as an RRSP?

Yes. There's no requirement to convert your entire RRSP into a RRIF all at once - you can convert only part of it, transfer that portion into a RRIF, and leave the remainder in your RRSP for the time being, provided the whole RRSP is eventually dealt with by the mandatory conversion age set out in the Income Tax Act. Partial conversions, multiple separate RRSPs, and partial transfers are all generally permitted.

This flexibility can be genuinely useful for planning purposes: converting only as much as you need to meet your current income requirements lets you keep the rest of your savings growing inside an RRSP for longer, rather than being forced into RRIF withdrawal rules, including the mandatory annual minimum, for money you don't yet need to access. It's worth keeping track of which portions have been converted and which haven't, since your RRIF minimum withdrawal obligation only applies to the RRIF portion, not to whatever remains in RRSP form. As the mandatory conversion age approaches, working out a sensible sequence for converting the rest is worth doing well in advance rather than leaving it to the deadline itself.