How can I recover corrupted Word files?

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Recently I have been digging for old Word (2013) files and I have found that some of them are corrupted. How this happened is a mystery to me, and if someone could comment I would appreciate it.

However, what I am concerned with is recovering some of them. Whereas some I can let go without much issue, others are very important. I would appreciate any help in recovering them, either with procedures I am yet unfamiliar with, or using specific software. Free would be preferable, but if best-in-class is pay and I need it, I’ll buy it.

Thanks for your opinions.

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