因为pdf.js这些年一直在发展，所以我想给予一个新的答案，就是可以在本地做，不需要涉及任何服务器或者外部服务，新的pdf.js有一个功能：getTextContent（）。你可以从中得到文本内容。我已经用下面的代码成功地做到了这一点。
1.你在每一步中得到的都是一个承诺。你需要这样编码：.then( function(){...})以继续下一步。

1. PDFJS.getDocument( data ).then( function(pdf) {
2. pdf.getPage(i).then( function(page){
3. page.getTextContent().then( function(textContent){
   1.最后得到的是一个字符串数组textContent.bidiTexts[]。将它们连接起来得到一页的文本。文本块的坐标用于判断是否需要插入换行符或空格。（这可能不完全健壮，但从我的测试来看似乎是可以的。）
   1.输入参数data需要是URL或ArrayBuffer类型的数据，我使用了FileReader API中的ReadAsArrayBuffer（file）函数来获取数据。

**注意：**根据其他用户的说法，库已更新并导致代码中断。根据下面 async5 的注解，您需要将textContent.bidiTexts替换为textContent.items。

function Pdf2TextClass(){
     var self = this;
     this.complete = 0;

    /**
     *
     * @param data ArrayBuffer of the pdf file content
     * @param callbackPageDone To inform the progress each time
     *        when a page is finished. The callback function's input parameters are:
     *        1) number of pages done;
     *        2) total number of pages in file.
     * @param callbackAllDone The input parameter of callback function is 
     *        the result of extracted text from pdf file.
     *
     */
     this.pdfToText = function(data, callbackPageDone, callbackAllDone){
     console.assert( data  instanceof ArrayBuffer  || typeof data == 'string' );
     PDFJS.getDocument( data ).then( function(pdf) {
     var div = document.getElementById('viewer');
    
     var total = pdf.numPages;
     callbackPageDone( 0, total );        
     var layers = {};        
     for (i = 1; i <= total; i++){
        pdf.getPage(i).then( function(page){
        var n = page.pageNumber;
        page.getTextContent().then( function(textContent){
          if( null != textContent.bidiTexts ){
            var page_text = "";
            var last_block = null;
            for( var k = 0; k < textContent.bidiTexts.length; k++ ){
                var block = textContent.bidiTexts[k];
                if( last_block != null && last_block.str[last_block.str.length-1] != ' '){
                    if( block.x < last_block.x )
                        page_text += "\r\n"; 
                    else if ( last_block.y != block.y && ( last_block.str.match(/^(\s?[a-zA-Z])$|^(.+\s[a-zA-Z])$/) == null ))
                        page_text += ' ';
                }
                page_text += block.str;
                last_block = block;
            }

            textContent != null && console.log("page " + n + " finished."); //" content: \n" + page_text);
            layers[n] =  page_text + "\n\n";
          }
          ++ self.complete;
          callbackPageDone( self.complete, total );
          if (self.complete == total){
            window.setTimeout(function(){
              var full_text = "";
              var num_pages = Object.keys(layers).length;
              for( var j = 1; j <= num_pages; j++)
                  full_text += layers[j] ;
              callbackAllDone(full_text);
            }, 1000);              
          }
        }); // end  of page.getTextContent().then
      }); // end of page.then
    } // of for
  });
 }; // end of pdfToText()
}; // end of class

我无法使gm 2008的示例工作（pdf.js上的内部数据结构发生了明显的变化），所以我编写了自己的完全基于承诺的解决方案，不使用任何DOM元素、queryselectors或canvas，使用mozilla示例中更新的pdf.js
因为我在node-webkit中使用它，所以它会吃掉上传的文件路径。你需要确保你下载了cmaps并指向某个地方，你需要pdf.js和pdf.worker.js来让它工作。

/**
     * Extract text from PDFs with PDF.js
     * Uses the demo pdf.js from https://mozilla.github.io/pdf.js/getting_started/
     */
    this.pdfToText = function(data) {

        PDFJS.workerSrc = 'js/vendor/pdf.worker.js';
        PDFJS.cMapUrl = 'js/vendor/pdfjs/cmaps/';
        PDFJS.cMapPacked = true;

        return PDFJS.getDocument(data).then(function(pdf) {
            var pages = [];
            for (var i = 0; i < pdf.numPages; i++) {
                pages.push(i);
            }
            return Promise.all(pages.map(function(pageNumber) {
                return pdf.getPage(pageNumber + 1).then(function(page) {
                    return page.getTextContent().then(function(textContent) {
                        return textContent.items.map(function(item) {
                            return item.str;
                        }).join(' ');
                    });
                });
            })).then(function(pages) {
                return pages.join("\r\n");
            });
        });
    }

用法：

self.pdfToText(files[0].path).then(function(result) {
      console.log("PDF done!", result);
 })

下面是一些JavaScript代码，使用http://hublog.hubmed.org/archives/001948.html中的Pdf.js可以完成您想要的任务：

var input = document.getElementById("input");  
var processor = document.getElementById("processor");  
var output = document.getElementById("output");  

// listen for messages from the processor  
window.addEventListener("message", function(event){  
  if (event.source != processor.contentWindow) return;  

  switch (event.data){  
    // "ready" = the processor is ready, so fetch the PDF file  
    case "ready":  
      var xhr = new XMLHttpRequest;  
      xhr.open('GET', input.getAttribute("src"), true);  
      xhr.responseType = "arraybuffer";  
      xhr.onload = function(event) {  
        processor.contentWindow.postMessage(this.response, "*");  
      };  
      xhr.send();  
    break;  

    // anything else = the processor has returned the text of the PDF  
    default:  
      output.textContent = event.data.replace(/\s+/g, " ");  
    break;  
  }  
}, true);

......这里有一个例子：
http://git.macropus.org/2011/11/pdftotext/example/

只留下一个完整的样本

<html>
    <head>
        <script src="https://npmcdn.com/pdfjs-dist/build/pdf.js"></script>
    </head>
    <body>
        <input id="pdffile" name="pdffile" type="file" />
        <button id="btn" onclick="convert()">Process</button>
        <div id="result"></div>
    </body>
</html>

<script>

    function convert() {
        var fr=new FileReader();
        var pdff = new Pdf2TextClass();
        fr.onload=function(){
            pdff.pdfToText(fr.result, null, (text) => { document.getElementById('result').innerText += text; });
        }
        fr.readAsDataURL(document.getElementById('pdffile').files[0])
        
    }

    function Pdf2TextClass() {
        var self = this;
        this.complete = 0;

        this.pdfToText = function (data, callbackPageDone, callbackAllDone) {
            console.assert(data instanceof ArrayBuffer || typeof data == 'string');
            var loadingTask = pdfjsLib.getDocument(data);
            loadingTask.promise.then(function (pdf) {

                var total = pdf._pdfInfo.numPages;
                //callbackPageDone( 0, total );        
                var layers = {};
                for (i = 1; i <= total; i++) {
                    pdf.getPage(i).then(function (page) {
                        var n = page.pageNumber;
                        page.getTextContent().then(function (textContent) {

                            //console.log(textContent.items[0]);0
                            if (null != textContent.items) {
                                var page_text = "";
                                var last_block = null;
                                for (var k = 0; k < textContent.items.length; k++) {
                                    var block = textContent.items[k];
                                    if (last_block != null && last_block.str[last_block.str.length - 1] != ' ') {
                                        if (block.x < last_block.x)
                                            page_text += "\r\n";
                                        else if (last_block.y != block.y && (last_block.str.match(/^(\s?[a-zA-Z])$|^(.+\s[a-zA-Z])$/) == null))
                                            page_text += ' ';
                                    }
                                    page_text += block.str;
                                    last_block = block;
                                }

                                textContent != null && console.log("page " + n + " finished."); //" content: \n" + page_text);
                                layers[n] = page_text + "\n\n";
                            }
                            ++self.complete;
                            //callbackPageDone( self.complete, total );
                            if (self.complete == total) {
                                window.setTimeout(function () {
                                    var full_text = "";
                                    var num_pages = Object.keys(layers).length;
                                    for (var j = 1; j <= num_pages; j++)
                                        full_text += layers[j];
                                    callbackAllDone(full_text);
                                }, 1000);
                            }
                        }); // end  of page.getTextContent().then
                    }); // end of page.then
                } // of for
            });
        }; // end of pdfToText()
    }; // end of class

</script>

注意：这段代码假设你使用的是nodejs，这意味着你解析的是本地文件而不是网页文件，因为最初的问题并没有明确询问解析网页上的pdf文件。
@gm2008的答案是一个很好的起点（请阅读它和它的评论以获得更多信息），但需要一些更新（08/19），并有一些未使用的代码。我也喜欢更完整的例子。有更多的重构和调整可以做（例如，与await），但现在它是尽可能接近原来的答案。
和以前一样，这里使用Mozilla的PDFjs库，npmjs包位于https://www.npmjs.com/package/pdfjs-dist。
根据我的经验，这在查找放置空格的位置方面做得不好，但这是另一个问题。
[Edit：我相信对.transform使用的更新已将空白恢复为原来的行为。]

// This file is called myPDFfileToText.js and is in the root folder
let PDFJS = require('pdfjs-dist');

let pathToPDF = 'path/to/myPDFfileToText.pdf';

let toText = Pdf2TextObj();
let onPageDone = function() {}; // don't want to do anything between pages
let onFinish = function(fullText) { console.log(fullText) };
toText.pdfToText(pathToPDF, onPageDone, onFinish);

function Pdf2TextObj() {
    let self = this;
    this.complete = 0;

    /**
     *
     * @param path Path to the pdf file.
     * @param callbackPageDone To inform the progress each time
     *        when a page is finished. The callback function's input parameters are:
     *        1) number of pages done.
     *        2) total number of pages in file.
     *        3) the `page` object itself or null.
     * @param callbackAllDone Called after all text has been collected. Input parameters:
     *        1) full text of parsed pdf.
     *
     */
    this.pdfToText = function(path, callbackPageDone, callbackAllDone) {
        // console.assert(typeof path == 'string');
        PDFJS.getDocument(path).promise.then(function(pdf) {

            let total = pdf.numPages;
            callbackPageDone(0, total, null);

            let pages = {};
            // For some (pdf?) reason these don't all come in consecutive
            // order. That's why they're stored as an object and then
            // processed one final time at the end.
            for (let pagei = 1; pagei <= total; pagei++) {
                pdf.getPage(pagei).then(function(page) {
                    let pageNumber = page.pageNumber;
                    page.getTextContent().then(function(textContent) {
                        if (null != textContent.items) {
                            let page_text = "";
                            let last_item = null;
                            for (let itemsi = 0; itemsi < textContent.items.length; itemsi++) {
                                let item = textContent.items[itemsi];
                                // I think to add whitespace properly would be more complex and
                                // would require two loops.
                                if (last_item != null && last_item.str[last_item.str.length - 1] != ' ') {
                                    let itemX = item.transform[5]
                                    let lastItemX = last_item.transform[5]
                                    let itemY = item.transform[4]
                                    let lastItemY = last_item.transform[4]
                                    if (itemX < lastItemX)
                                        page_text += "\r\n";
                                    else if (itemY != lastItemY && (last_item.str.match(/^(\s?[a-zA-Z])$|^(.+\s[a-zA-Z])$/) == null))
                                        page_text += ' ';
                                } // ends if may need to add whitespace

                                page_text += item.str;
                                last_item = item;
                            } // ends for every item of text

                            textContent != null && console.log("page " + pageNumber + " finished.") // " content: \n" + page_text);
                            pages[pageNumber] = page_text + "\n\n";
                        } // ends if has items

                        ++self.complete;

                        callbackPageDone(self.complete, total, page);

                        // If all done, put pages in order and combine all
                        // text, then pass that to the callback
                        if (self.complete == total) {
                            // Using `setTimeout()` isn't a stable way of making sure 
                            // the process has finished. Watch out for missed pages.
                            // A future version might do this with promises.
                            setTimeout(function() {
                                let full_text = "";
                                let num_pages = Object.keys(pages).length;
                                for (let pageNum = 1; pageNum <= num_pages; pageNum++)
                                    full_text += pages[pageNum];
                                callbackAllDone(full_text);
                            }, 1000);
                        }
                    }); // ends page.getTextContent().then
                }); // ends page.then
            } // ends for every page
        });
    }; // Ends pdfToText()

    return self;
}; // Ends object factory

在终端中运行：
node myPDFfileToText.js

2021年2月更新

<script src="https://npmcdn.com/pdfjs-dist/build/pdf.js"></script>
    <script>
    
function Pdf2TextClass(){
    var self = this;
    this.complete = 0;

    this.pdfToText = function(data, callbackPageDone, callbackAllDone){
    console.assert( data  instanceof ArrayBuffer  || typeof data == 'string' );
    var loadingTask = pdfjsLib.getDocument(data);
    loadingTask.promise.then(function(pdf) {

    var total = pdf._pdfInfo.numPages;
    //callbackPageDone( 0, total );        
    var layers = {};        
    for (i = 1; i <= total; i++){
       pdf.getPage(i).then( function(page){
       var n = page.pageNumber;
       page.getTextContent().then( function(textContent){
       
       //console.log(textContent.items[0]);0
         if( null != textContent.items ){
           var page_text = "";
           var last_block = null;
           for( var k = 0; k < textContent.items.length; k++ ){
               var block = textContent.items[k];
               if( last_block != null && last_block.str[last_block.str.length-1] != ' '){
                   if( block.x < last_block.x )
                       page_text += "\r\n"; 
                   else if ( last_block.y != block.y && ( last_block.str.match(/^(\s?[a-zA-Z])$|^(.+\s[a-zA-Z])$/) == null ))
                       page_text += ' ';
               }
               page_text += block.str;
               last_block = block;
           }

           textContent != null && console.log("page " + n + " finished."); //" content: \n" + page_text);
           layers[n] =  page_text + "\n\n";
         }
         ++ self.complete;
         //callbackPageDone( self.complete, total );
         if (self.complete == total){
           window.setTimeout(function(){
             var full_text = "";
             var num_pages = Object.keys(layers).length;
             for( var j = 1; j <= num_pages; j++)
                 full_text += layers[j] ;
             console.log(full_text);
           }, 1000);              
         }
       }); // end  of page.getTextContent().then
     }); // end of page.then
   } // of for
 });
}; // end of pdfToText()
}; // end of class
var pdff = new Pdf2TextClass();
pdff.pdfToText('PDF_URL');
    </script>

对于所有实际希望在节点服务器上使用它的人：

/**
 * Created by velten on 25.04.16.
 */
"use strict";
let pdfUrl = "http://example.com/example.pdf";
let request = require('request');
var pdfParser = require('pdf2json');

let pdfPipe = request({url: pdfUrl, encoding:null}).pipe(pdfParser);

pdfPipe.on("pdfParser_dataError", err => console.error(err) );
pdfPipe.on("pdfParser_dataReady", pdf => {
    //optionally:
    //let pdf = pdfParser.getMergedTextBlocksIfNeeded();

    let count1 = 0;
    //get text on a particular page
    for (let page of pdf.formImage.Pages) {
        count1 += page.Texts.length;
    }

    console.log(count1);
    pdfParser.destroy();
});

有可能，但：

• 无论如何，你都必须使用服务器，你不可能在用户计算机上获得文件的内容，而不将其传输到服务器并返回
• 我想还没有人写过这样的库

所以如果你有一些空闲时间你可以学习pdf格式并自己写这样一个库，或者你当然可以只使用服务器端库。