Learn
Plain-language explainers on why PDFs get large, how compression works, KB vs MB upload limits, and whether online PDF tools are safe.
Why is my PDF so large?A PDF is usually large because its pages are high-resolution images — a phone photo of one page can be 3–8MB. Other causes are scanning at 600 DPI, colour instead of grayscale, embedded fonts, and duplicate images. Re-rendering pages at 100–150 DPI as JPEG typically cuts the size by 80–95%.KB vs MB: how upload size limits are counted1MB is 1,024KB in most upload portals and operating systems, and 1KB is 1,024 bytes — but some systems use 1,000. Because of this, a file shown as 300KB on your phone might be 307,200 bytes, which a strict 300,000-byte check rejects. Aim about 5–10% under the stated limit to be safe.How PDF compression worksPDF compressors shrink scanned PDFs by re-rendering each page at a lower resolution (DPI) and saving it as a JPEG at a chosen quality. File size scales roughly with the square of DPI, so going from 300 to 150 DPI cuts size by about 75%. Target-size tools search DPI and quality automatically until the file fits.Are online PDF tools safe for ID documents?Most online PDF tools upload your file to their servers, where it may be stored temporarily. In-browser tools like FramePDF's process the file on your own device with JavaScript, so it never leaves your computer or phone. For ID documents, prefer in-browser tools or an offline app.