Guides
ガイド
ブラウザ上でファイルを安全に扱うための実践的なガイドとインサイト。各記事から直接ツールへアクセスできます。
When the Hometax e-Tax Invoice Secure Mail (NTS_eTaxInvoice.html) Won't Open
Why the HTML attachment from Korea's National Tax Service shows only a blank page or garbled text, and how to enter the password and read it in the browser with nothing to install. Limits stated plainly.
How to Check a Korean Digital Certificate's Expiry — Open signCert.der
How to see when your Korean joint certificate (formerly 'public certificate') expires before logging in to a bank or Hometax. Open signCert.der from the NPKI folder in the browser to see the validity period and issuer. No password needed.
How to Cut an MP3 — Trim Just the Part You Need, No Software (Ringtones, Highlights)
Trim MP3, M4A, or WAV to the section you need: pick the range on a waveform, add fades, make a ringtone. No install, no sign-up, no upload — it runs in the browser. What happens to audio quality is explained too.
How to Sign a PDF — Add a Handwritten Signature Without Printing or Scanning
How to sign a contract or consent form PDF you received by email and send it back: draw with a mouse or finger, or place a signature image, on the page and position you choose, then save a new PDF. No upload. Includes an honest note on legal validity.
Resize an Image to Exact Pixels — Set the Width and Height You Need
How to fit a photo to a required pixel size — ID photo specs, shop thumbnails, upload limits. Shrink without distortion using the ratio lock, and handle specs like 300×400 with crop plus resize. In the browser, no upload.
How to Add a Stamp to a PDF — Make a Seal Image and Place It Where You Need
Two steps to stamp a PDF quote, contract, or form: make a seal image (transparent PNG) from a name, then place it on the page and position you want with the PDF Sign tool and save. Using an existing stamp, and how this differs from a registered seal.
How to Watermark a Video — Channel Name or Logo, WYSIWYG
Stamp a copyright line or logo onto a video before sharing it. Position (9 spots), size and opacity adjust with a live preview, and the video is never uploaded.
How to Make a YouTube Thumbnail from Your Video — No Design App Needed
Pause on the best frame of your video, capture it, add a title, and save a 1280×720 thumbnail. Style presets give it structure even without design skills.