A corrupted PDF may refuse to open, open with missing pages, display 'file is damaged' errors, render garbled content, or crash the PDF viewer. The degree of corruption determines how much can be recovered — from a complete fix with no content loss, to partial recovery of some pages, to no recovery at all.
Common causes of PDF corruption
Incomplete download or transfer: if the download was interrupted (browser closed mid-download, connection dropped), the file is truncated. The PDF header may be intact but the content is missing past the truncation point. Partial recovery is often possible.
Storage media failure: files on failing drives or corrupted SD cards may have data written incorrectly. The damage is at the byte level and may affect any part of the file.
Email or compression artefacts: some email servers modify binary attachments, and some compression programs corrupt the PDF structure when extracting. Re-downloading from the source often resolves this.
Software bugs: some tools (older converters, scanner firmware) produce PDFs with structural errors — cross-reference table errors, incorrect object offsets, invalid page dictionaries. These are often recoverable because the content is present but the index is wrong.
What repair tools can and cannot fix
Repairable: cross-reference table errors, incorrect object offsets, minor structural inconsistencies, invalid metadata. Most PDF repair tools rebuild the cross-reference table from scratch by scanning the file for valid objects — this is the core repair operation.
Partially repairable: truncated files. If the PDF was cut off partway through, everything before the truncation point can often be recovered. Pages after the truncation are lost.
Not repairable: files with completely corrupted content data. If the pixel data for an embedded JPEG is corrupted, the image cannot be reconstructed. If the text stream is damaged, the text on those pages is lost. Repair can recover the structure; it cannot reconstruct destroyed content.
Before using a repair tool
Check for the original: if the PDF was received by email, downloaded from a website, or exported from software, re-downloading or re-exporting often produces a clean file. Repair should be a last resort when the original source is unavailable.
Try a different PDF viewer: what appears to be a corrupted file sometimes opens correctly in a different viewer. Adobe Acrobat is the most tolerant; Preview (Mac), Evince (Linux), and browser-based viewers have different compatibility profiles.
Check the file size: a legitimate PDF is rarely under 5KB. A 0KB or tiny file indicates either an empty file or a failed download, not a corrupted PDF.
Using Filum's Repair PDF tool
Upload the damaged PDF. Filum attempts to rebuild the PDF structure, recover readable pages, and produce a valid output file. Not every file can be repaired — if the content itself is destroyed rather than just the structure, the tool will output what it can recover. The file is processed on a secure server and deleted immediately after conversion.