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Repair PDF

Rebuild a corrupted or unreadable PDF.

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PDF · up to 100MB per file

About Repair PDF

A PDF that will not open is usually not destroyed — it is structurally inconsistent. An interrupted download, a failed sync, or a buggy generator leaves the cross-reference table pointing at the wrong offsets, and strict readers refuse to open the file even though the page data is intact.

Repair parses the file leniently, recovers the objects it can read, and writes out a fresh, well-formed document.

How to use Repair PDF

  1. Step 1

    Upload the damaged PDF

    Add the file that will not open properly.

  2. Step 2

    Rebuild

    Readable objects are recovered and written into a clean structure.

  3. Step 3

    Download and check

    Open the repaired file and verify the pages you need.

When it helps

  • Opening a file that a reader rejects as damaged or invalid.
  • Recovering a document truncated by a failed download.
  • Fixing a PDF produced by an old or non-standard exporter.
  • Rescuing a file from a corrupted USB drive or backup.

Good to know

  • Repair recovers what is still present in the file. Pages that were never downloaded cannot be reconstructed.
  • If a file was truncated at 60%, expect roughly the first 60% of pages back.
  • Always keep the damaged original until you have confirmed the repair.

Repair PDF: frequently asked questions

How edits are written into a PDF

Layers, not overwrites

PDF was designed as a final-form format: the page describes where every glyph sits, not what the paragraph means. Editing tools therefore work by adding a new layer of drawing instructions on top of the existing content stream — a stamp, a page number, a signature image, a rectangle of colour.

Because the addition sits above the original, the underlying text stays searchable and selectable. That is a feature when you are numbering pages, and something to be aware of when you are covering information: a coloured box hides text visually but does not delete it. Flatten or rasterise the page when the content must genuinely be gone.

Coordinates, points and the bottom-left origin

PDF measures everything in points, where 72 points equal one inch, and its coordinate origin sits at the bottom-left of the page rather than the top-left used by screens. An A4 page is 595 × 842 points; US Letter is 612 × 792.

This is why a margin that looked right on a Letter document shifts slightly on A4, and why placing an element 'twenty from the top' requires subtracting from the page height. Tools that offer margin or position presets handle the arithmetic for you, but knowing the units helps when you need an exact placement.

Fonts, embedding and why text can change appearance

Any text added to a page needs a font program. If the font is embedded, the document renders identically everywhere; if it is merely referenced, the reader substitutes something similar and spacing can shift. Standard base-14 fonts such as Helvetica and Times are assumed to exist in every reader, which is why added labels commonly use them.

Non-Latin scripts are the usual sticking point: a base font that lacks Cyrillic, Arabic or CJK glyphs will render them as blanks or boxes. Keep added annotations in the Latin alphabet, or convert the finished page to an image, when a document must be reproduced exactly on unknown systems.

Common problems and fixes

Added text or numbers overlap existing content
The source pages already use the margin area. Increase the margin setting, move the element to the opposite corner, or add a small white backing box first.
The change is invisible in the preview but present in the file
Browser preview panes cache aggressively. Download the result and open it in a desktop reader before concluding the edit failed.
The edited file is much larger than the original
Raster elements such as signature photographs are stored at full resolution. Crop and shrink the source image, or run a compression pass afterwards.

Terms worth knowing

Flattening
Merging annotations, form fields and overlays permanently into the page content so they can no longer be edited or removed.
Point
The PDF unit of length: 1/72 of an inch, so 72 points make one inch.
Base-14 fonts
The fourteen typefaces every conforming PDF reader must provide, including Helvetica, Times and Courier.

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