Opening a sealed envelope without tearing it can be a challenge, and due to differences in the type of glue, no one method will work for every letter. Work slowly and calmly, or you'll only end up with scraps of paper and regret. Try this
How to Fold an Origami Envelope (with Pictures) - wikiHow
How to Fold an Origami Envelope (with Pictures) - wikiHow
4 Ways to Open a Sealed Envelope - wikiHow
How to Fold an Origami Envelope (with Pictures) - wikiHow
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How to Secretly Open a Sealed Envelope: 9 Steps (with Pictures)
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4 Ways to Open a Sealed Envelope - wikiHow
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4 Ways to Open a Sealed Envelope - wikiHow
4 Ways to Open a Sealed Envelope - wikiHow
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3 Ways to Fold and Insert a Letter Into an Envelope - wikiHow