求翻译：我们随信附寄编号为CTC5236的购买合同一式两份，会签后请归还一份以便存档；是什么意思？

We enclose herewith the number CTC5236 purchase contract in duplicate, please return a countersigned for archiving;

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We enclose the serial number along with the letter are CTC5236 purchase contract type two, after countersigns please do return one in order to archive;

We have enclosed two copies of the purchase contract number CTC5236, sign and return one copy for archiving;

We enclose and number the purchase contract that is CTC5236 in duplicate with the letter, please return one in order to file after countersigning;