Settled is the rule in our jurisdiction that a notarized document has in its favor the presumption of regularity, and to overcome the same, there must be evidence that is clear, convincing and more than merely preponderant; otherwise the document should be upheld. Clearly, the positive presumption of the due execution of the subject real estate mortgage outweighs [petitioners'] bare and unsubstantiated denial that the parcels of land covered by TCT Nos. T-225132 and T-225131 were among those intended to secure the loan of One Million Pesos.  Their imputation of fraud among the officials of [the bank] is weak and unpersuasive. x x x