Zig Requires Chilkat v11.7.0+

Remove a PDF's Old Revisions

See more PDF Optimization Examples

Demonstrates dropOldRevisions. A PDF that has been edited and saved several times carries every earlier revision: the superseded objects are still in the file, reachable through the older cross-reference sections. The audit reports them as "oldRevisions", and dropping them is often the single largest saving in a real document. Dropping them requires a full rewrite, which is why it invalidates existing digital signatures. Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // The PDF used in this example is available at grand_canyon_hiking_guide.pdf

    const pdf = try chilkat.Pdf.init();
    defer pdf.deinit();
    pdf.loadFile("qa_data/pdf/grand_canyon_hiking_guide.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // How much of this file is superseded revisions?
    const json = try chilkat.JsonObject.init();
    defer json.deinit();
    const json_out = try chilkat.JsonObject.init();
    defer json_out.deinit();
    pdf.optimize("audit", json, json_out) catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("fileSize:     {d}\n", .{json_out.intOf("fileSize")});
    std.debug.print("oldRevisions: {d}\n", .{json_out.intOf("usage.oldRevisions.bytes")});

    // Drop them, and nothing else, so that the saving is attributable.
    json.updateBool("compressUncompressed", false) catch {};
    json.updateBool("recompressFlate", false) catch {};
    json.updateBool("replaceLegacyFilters", false) catch {};
    json.updateBool("imagePredictors", false) catch {};
    json.updateBool("dedupeStreams", false) catch {};
    json.updateBool("dedupeObjects", false) catch {};
    json.updateBool("removeUnreferenced", false) catch {};
    json.updateBool("removeUnusedResources", false) catch {};
    json.updateBool("removeUnusedLayers", false) catch {};
    json.updateBool("coalesceContent", false) catch {};
    json.updateBool("tidyContent", false) catch {};
    json.updateBool("subsetFonts", false) catch {};
    json.updateBool("dropOldRevisions", true) catch {};

    pdf.optimize("optimize", json, json_out) catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    pdf.writeFile("qa_output/grand_canyon_one_revision.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // The saving is an estimate: what the old revisions occupied is known exactly, but the writer
    // decides the final layout.  Measure the written file for the real number.
    const fac = try chilkat.FileAccess.init();
    defer fac.deinit();
    std.debug.print("bytesSaved (reported): {d}\n", .{json_out.intOf("bytesSaved")});
    std.debug.print("written file:          {d}\n", .{fac.fileSize("qa_output/grand_canyon_one_revision.pdf")});
}