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Validate a document before accepting it

This guide shows how to check a PDF you received — an upload, an attachment, a supplier's invoice — before it enters your system, and how to act on the verdict.

Validate the document​

Create one validator and keep it: it holds no state, so a single instance serves every thread and can be registered as a singleton. Open the document, validate it, and decide on the report:

using AdCodicem.Pdf.Documents;
using AdCodicem.Pdf.Validation;

var validator = new PdfValidator();

using var document = PdfDocument.Open("received-from-supplier.pdf");
var report = validator.Validate(document);

if (report.HasErrors)
{
    // The reader cannot vouch that it reads this document as written: refuse it, or send it to repair.
}
else
{
    // Accept it. Warnings, if any, break the specification in ways every reader reads past: keep the report.
}

The document stays open after validation, and is yours to dispose.

Tell the sender what is wrong​

Every finding says which rule found it, where, what is wrong, and what would put it right:

foreach (var finding in report.Findings)
{
    Console.WriteLine(finding);          // Error file.startxref-missing at offset 213: …
    Console.WriteLine(finding.Remedy);   // Write startxref and the offset of …
}

A finding about a page gives the page, from 0, in finding.Location.PageIndex; written out, it counts from 1.

Filter by rule​

Filter on the rule identifier, never on the message: identifiers are public API, and stay the same from one release to the next. PdfValidationRuleIds holds each as a constant.

if (report.Contains(PdfValidationRuleIds.FileEofMissing))
{
    // The file may have been cut short in transit.
}

foreach (var finding in report.Findings)
{
    if (finding.RuleId.StartsWith("page-tree.", StringComparison.Ordinal))
    {
        Console.WriteLine(finding);
    }
}

Bound the report​

A hostile file can have a fault in every object. A report keeps 1,000 findings by default and counts the rest; lower the bound when you only need a verdict, and check SuppressedCount when you need to know how many you did not keep:

var validator = new PdfValidator(new PdfValidatorOptions { FindingCapacity = 100 });

ErrorCount, WarningCount and InformationCount count every finding, kept or not, so HasErrors is right however small the bound.

Check a large document whole​

Validation reads under the document's reader limits. When a finding says, as information, that an object could not be checked whole, the reader cut it at a limit: open the document with that limit raised and validate again (Read or refuse a document that reaches a limit). If you opened the document with ThrowOnLimit, Validate throws PdfLimitExceededException instead.

See also​