Of course, Adobe is going to be the premiere here but is neither open source, nor free. It used to be integrated into Apple universe devices for free until very recently. Monster pdf is not free but very full function.
IMO pdf escape is probably the best editor out there and mostly because it supports an erase function. Also, not free. (see below)
I pay for Adobe Pro DC which is priced pretty poorly but does the hands down best and lowest click count operation involving converting and compressing photos from jpeg to pdf. My single biggest gripe right this second is that for the cost ($20/m) it cannot handle HEIC. To work with that I have to use Paint to convert one at a time, very cludgy process, and then put into Adobe to finish. The compression program is invaluable to us.
I pay for Adobe, the office manager pays for pdfescape such that the very few things I cannot do I can send over to them.
As far as truly free there is stuff like pdf rabbit (if still around) but you have to upload and download one at a time over a very insecure ad filled pop up infested web browser. Others I have experienced are very similar. pdfescape used to let you do several a month free. We surpass that but if your need isn't very high you might squeak by.
They have also been trying dochub which I don't know much about yet but has so far remained free and fairly high volume.