My former company has asked me to sign several patent assignments since I left the company but they only ever send me the final signature page. I didn't care about signing the ones I knew about when I left, but they have begun sending me new patents that partially overlap my old work. I don't even know what they encompass and they will not send me the patent itself because I work for a company that is something of a competitor. They tell me this is standard practice and I am legally required to sign, but this seems very sketchy. Is this true? Can I be obligated to sign a patent assignment without knowing what is in it?
Regardless of any other contract, it is illegal in any "civilized" country to be forced to sign a blank paper.
You should talk to a lawyer, about the signatures which you provided already, and for the future ones.
High stakes contracts are signed on all sheets, even on all pages, by all parties, just for the purpose to prove that reading of the content was possible.
Bottom line: never sign anything which is not very clear to you - let alone (more or less) blank pages.
You probably signed an employment agreement in which you agreed to sign the assignments (or state law has that effect). I think it is ridiculous not to send you the whole assignment agreement. You might try saying that you know you are obliged to sign assignments but how do you even know if you are signing an assignment.
Since the AIA patent law of 2012 went into effect, the inventor's signature is a little less important. If the company has a blanket agreement from you to assign, they can file without you by establishing that you have that obligation but they couldn't find you or you otherwise will not sign. I'm a patent agent and this is really a question for an attorney so you might want to look up the provisions of the American Invents Act.