Check if a pdf file is valid using PdfBox by Apache

Question

I am using PdfBox in Java to extract text from PDF files. Some of the input files provided are not valid and PDFTextStripper halts on these files. Is there a clean way to check if the provided file is indeed a valid PDF?

Answer 1

Pdf files begin "%PDF" (open one in TextPad or similar and take a look)

Any reason you can't just read the file with a StringReader and check for this?

Answer 2

What do you mean by a valid PDF file? It also needs to contain a valid data reference table correctly pointing to all the objects in the file.

Answer 3

you can find out the mime type of a file (or byte array), so you dont dumbly rely on the extension. I do it with aperture's MimeExtractor (http://aperture.sourceforge.net/) or I saw some days ago a library just for that (http://sourceforge.net/projects/mime-util)

I use aperture to extract text from a variety of files, not only pdf, but have to tweak thinks for pdfs for example (aperture uses pdfbox, but i added another library as fallback when pdfbox fails)

Answer 4

Here is what I use into my NUnit tests, that must validate against multiple versions of PDF generated using Crystal Reports:

public static void CheckIsPDF(byte[] data)
    {
        Assert.IsNotNull(data);
        Assert.Greater(data.Length,4);

        // header 
        Assert.AreEqual(data[0],0x25); // %
        Assert.AreEqual(data[1],0x50); // P
        Assert.AreEqual(data[2],0x44); // D
        Assert.AreEqual(data[3],0x46); // F
        Assert.AreEqual(data[4],0x2D); // -

        if(data[5]==0x31 && data[6]==0x2E && data[7]==0x33) // version is 1.3 ?
        {                  
            // file terminator
            Assert.AreEqual(data[data.Length-7],0x25); // %
            Assert.AreEqual(data[data.Length-6],0x25); // %
            Assert.AreEqual(data[data.Length-5],0x45); // E
            Assert.AreEqual(data[data.Length-4],0x4F); // O
            Assert.AreEqual(data[data.Length-3],0x46); // F
            Assert.AreEqual(data[data.Length-2],0x20); // SPACE
            Assert.AreEqual(data[data.Length-1],0x0A); // EOL
            return;
        }

        if(data[5]==0x31 && data[6]==0x2E && data[7]==0x34) // version is 1.4 ?
        {
            // file terminator
            Assert.AreEqual(data[data.Length-6],0x25); // %
            Assert.AreEqual(data[data.Length-5],0x25); // %
            Assert.AreEqual(data[data.Length-4],0x45); // E
            Assert.AreEqual(data[data.Length-3],0x4F); // O
            Assert.AreEqual(data[data.Length-2],0x46); // F
            Assert.AreEqual(data[data.Length-1],0x0A); // EOL
            return;
        }

        Assert.Fail("Unsupported file format");
    }