For clarification:
In the strict sense, technically the PR card is indeed a Travel Document, actually that is precisely what it is, a Travel Document, even though it is a Travel Document with very limited validity, which is to say it is only recognized as a valid Travel Document by Canada (well, there may be some countries which recognize it as such, but it is not generally recognized as a TD outside Canada). That said, many agencies in Canada (federal and provincial) recognize the PR card as proof of immigration status in Canada.
BTW: in the dozens of times I returned to Canada while I was a PR, I never once presented any additional documentation at the POE, only my PR card. The border officers have discretion to ask for additional documentation, including in particular additional identification, including passports. Since the PR card is only recognized by Canada, PRs traveling outside Canada necessarily must be in possession of some other Travel Document, which usually (except in private land crossings with the U.S.) means a passport. So border officers know the PR returning to Canada must be in possession of such other Travel Document and it would not be unusual to require the traveler to present it . . . but, as I said, in dozens of times returning to Canada, I only presented my PR card and I was never asked for anything more.
As most of us here have posted, it is correct that the expired PR card does not mean PR has expired.
But it is not true that a PR abroad without a currently valid PR card can just to to the nearest Canadian embassy and immediately be issued a "visa."
In fact, as most others have pointed out, what the PR abroad needs to board commercial transportation destined for Canada is a PR Travel Document, which is indeed obtained at the nearest Canadian embassy, but which must be applied for and, given the presumption that in the absence of a valid PR card there is a presumption the individual does not have valid PR status, that application needs to be accompanied by proof of compliance with the PR residency obligation. And it usually takes a significant period of time to process, many days at minimum in most embassies.
