Dear Ellundula,
It is not illegal, but it is illegitimate to do so. I have time and again stated that recruitment comes under the ambit of business risk. Without taking these risks, no company can function effectively at any time.
If a document is misplaced or damaged, the person to whom the document belongs can sue your company for negligence and also for theft. In such a case, the directors would be held accountable.
Just because a few HR people started a certain practice does not mean we have to follow the same. If there is a need to follow a practice, it should be one that is good and sustainable.
By collecting original documents, the company is not only increasing its recruitment and asset management costs but also incurring additional legal liability that is unnecessary.
In any case, the company cannot retain any of the original documents even if the candidate leaves the company without proper formalities because, according to the law, the employee owns the certificate, and you are merely a caretaker to whom it has been entrusted for safekeeping.
Therefore, consider whether your company wants to face all these troubles or maintain a clean and free recruitment process.
Regards,
Octavious