如何使用iTextSharp读取无页眉页脚文件及移除现有PDF页眉页脚

Alright, let's tackle these two common iTextSharp tasks you're asking about—extracting text without headers/footers, and removing headers/footers from existing PDFs. I'll walk through each scenario with practical code examples and notes for edge cases (like files that might not have headers/footers at all).

1. Extract Text Excluding Headers and Footers #

The default LocationTextExtractionStrategy pulls all text from a page, including headers and footers. To get only the main content, you'll need to create a custom extraction strategy that filters text based on its position on the page. Headers/footers are almost always in fixed top/bottom regions, so we can use coordinate bounds to exclude them.

First, define your custom strategy:

public class FilteredTextExtractionStrategy : LocationTextExtractionStrategy
{
    private readonly float _headerHeight;
    private readonly float _footerHeight;
    private readonly float _pageHeight;

    public FilteredTextExtractionStrategy(float headerHeight, float footerHeight, float pageHeight)
    {
        _headerHeight = headerHeight;
        _footerHeight = footerHeight;
        _pageHeight = pageHeight;
    }

    public override void RenderText(TextRenderInfo renderInfo)
    {
        // Get the bottom y-coordinate of the text chunk
        float textBottom = renderInfo.GetDescentLine().GetStartPoint()[1];
        
        // Only process text that's below the header and above the footer
        if (textBottom > _footerHeight && textBottom < (_pageHeight - _headerHeight))
        {
            base.RenderText(renderInfo);
        }
    }
}

Then use this strategy to extract text. Adjust the header/footer height values to match your actual PDF's layout:

using (PdfReader reader = new PdfReader("your-file-path.pdf"))
{
    // Define header/footer heights (tweak these based on your document)
    float headerHeight = 50f; 
    float footerHeight = 50f;
    int pageNumber = 1; // Target page number

    // Get the page's total height
    Rectangle pageSize = reader.GetPageSize(pageNumber);
    float pageHeight = pageSize.Height;

    // Extract text excluding header/footer regions
    string cleanText = PdfTextExtractor.GetTextFromPage(
        reader, 
        pageNumber, 
        new FilteredTextExtractionStrategy(headerHeight, footerHeight, pageHeight)
    );

    // Use your clean text here
}

Quick Note: #

If the PDF has no headers/footers, this code still works flawlessly—it just extracts all the text since there's no content in the excluded regions. For variable PDFs, you could add logic to auto-detect header/footer bounds, but fixed values work for most standard documents.

2. Remove Headers and Footers from an Existing PDF #

To permanently strip headers/footers, create a new PDF that copies the original page content but crops out the header/footer regions. We'll use PdfStamper for this straightforward approach:

using (PdfReader reader = new PdfReader("original-file.pdf"))
using (PdfStamper stamper = new PdfStamper(reader, new FileStream("cleaned-file.pdf", FileMode.Create)))
{
    float headerHeight = 50f;
    float footerHeight = 50f;

    for (int i = 1; i <= reader.NumberOfPages; i++)
    {
        Rectangle originalPageSize = reader.GetPageSize(i);
        
        // Calculate the new crop area: exclude top header and bottom footer
        Rectangle newCropBox = new Rectangle(
            originalPageSize.Left,
            originalPageSize.Bottom + footerHeight,
            originalPageSize.Right,
            originalPageSize.Top - headerHeight
        );

        // Apply the crop box to the page
        stamper.GetUnderContent(i).SetCropBox(newCropBox);
        stamper.GetOverContent(i).SetCropBox(newCropBox);
        stamper.SetPageSize(newCropBox, i);
    }
}

Alternative: Redraw Page Content (For Overlapping Content) #

If cropping isn't enough (e.g., headers/footers overlap with main content), redraw the page content onto a new canvas, only including the middle region:

using (PdfReader reader = new PdfReader("original-file.pdf"))
using (Document document = new Document())
using (PdfWriter writer = PdfWriter.GetInstance(document, new FileStream("cleaned-file.pdf", FileMode.Create)))
{
    document.Open();
    float headerHeight = 50f;
    float footerHeight = 50f;

    for (int i = 1; i <= reader.NumberOfPages; i++)
    {
        Rectangle originalPage = reader.GetPageSize(i);
        // Set new document size to exclude header/footer
        document.SetPageSize(new Rectangle(
            originalPage.Left,
            originalPage.Bottom + footerHeight,
            originalPage.Right,
            originalPage.Top - headerHeight
        ));
        document.NewPage();

        // Import and redraw the original page content
        PdfImportedPage importedPage = writer.GetImportedPage(reader, i);
        // Offset content to skip footer region
        float yOffset = -footerHeight;
        writer.DirectContent.AddTemplate(importedPage, 0, yOffset);
    }
    document.Close();
}

Quick Note: #

If the original PDF has no headers/footers, this code just creates an exact copy—so it's safe to run on all your target files regardless of their layout.

内容的提问来源于stack exchange，提问作者shmookh