PDF is a binary coded format generated by virtual printing of various files. Since most of PDF data is compressed, editing PDF files with a text editor will cause data error, or lose part of the data due to network instability during network transfer, which will cause PDF files to be damaged and corrupt. PDF readers and viewers cannot open or repair those corrupt PDF files and would throw out a few error alerts.
PDF Fixer is a free PDF repair utility which fixes corrupt PDF files by restructuring the damaged PDF data, rebuilding XREF tables and then recovers those PDF documents back.
There are some command-line tools like PDFTK and Ghostscript both have the PDF fixing function, however, PDFTK just can fix PDF metadata errors and Ghostscript can only regenerate XREF tables. Once users need to repair a really damaged PDF file, they will find PDFTK and Ghostscript cannot recover the file data and display errors. Different from these two tools, PDF Fixer analyzes the data that still exists through the whole corrupt PDF and assembles objects to repair it out. It will repair a lot of PDF files which PDFTK and Ghostscript cannot fix.
PDF Fixer also has the multi-thread feature, which enables users to fix multiple PDF files at once.