Property "password" does not exists on type Document

You need to add type here with pre-save hook as per the mongoose docs, pre hook is defined as,

/**
 * Defines a pre hook for the document.
 */
pre<T extends Document = Document>(
  method: "init" | "validate" | "save" | "remove",
  fn: HookSyncCallback<T>,
  errorCb?: HookErrorCallback
): this;

and if you have an interface like below then,

export interface IUser {
  email: string;
  password: string;
  name: string;
}

Add type with pre-save hook,

userSchema.pre<IUser>("save", function save(next) { ... }

I dont know if this will help as the question is old now, however I tried this

import mongoose, { Document } from 'mongoose';

const User = mongoose.model<IUser & Document>("users", UserSchema);

type IUser = {
    username: string
    password: string
}

mongoose.model needs a Document type, and you want to extend that document, therefore Unify the two types

you can also pass the interface type to the schema itself.

import { model, Schema, Document } from 'mongoose';

const userSchema = new mongoose.Schema<IUser>({
  email: { type: String, required: true, unique: true },
  password: { type: String, required: true },
  name: { type: String, required: true }
});

interface IUser extends Document{
  email: string;
  password: string;
  name: string;
}