Homelab, Linux & ABAP (~˘▾˘)~
 

[PDF.js] Set light and dark theme manually

The new PDF.js viewer design Photon supports a light and a dark mode. By default, the theme is set automatically. To overwrite this, you can set the viewerCssTheme property.

I’ve embedded my PDF viewer in an iFrame like this:

<iframe id="pdf-js-viewer" src="/pdf/web/viewer.html" title="webviewer" frameborder="0" width="100%" height="700" allowfullscreen="" webkitallowfullscreen=""/>

By setting the viewerCssTheme property, you are able to change the PDF viewer theme. It can be modified using the PDFViewerApplicationOptions.set() function and there are three possible values. The property has to be set before the Viewer is initialized. To archive this, you can listen to the event webviewerloaded (read more about it here). In my case, I also had to call _forceCssTheme() after that.

                document.addEventListener("webviewerloaded", async () => {
                    let pdfViewerIFrame = document.getElementById("pdf-js-viewer")
                    pdfViewerIFrame.onload = () => {
                        // https://github.com/mozilla/pdf.js/blob/master/web/app_options.js
                        pdfViewerIFrame.contentWindow.PDFViewerApplicationOptions.set("viewerCssTheme", 1)       // 0=automatic theme, 1=light theme, 2=dark theme 
                        pdfViewerIFrame.contentWindow.PDFViewerApplication._forceCssTheme()
                    }
                })

[PDF.js] Allow PDF documents to disable copying in the viewer

With pull request 11789, the PDF Viewer respects the PDF property Content Copying, if the viewer option enablePermissions is set to true.

I’ve embedded my viewer in an iFrame like this:

<iframe id="pdf-js-viewer" src="/pdf/web/viewer.html" title="webviewer" frameborder="0" width="100%" height="700" allowfullscreen="" webkitallowfullscreen=""/>

The enablePermissions property can be modified using the PDFViewerApplicationOptions.set() function. The property has to be set before the Viewer is initialized. To archive this, you can listen to the event webviewerloaded (read more about it here).

                document.addEventListener("webviewerloaded", async () => {
                    let pdfViewerIFrame = document.getElementById("pdf-js-viewer")
                    pdfViewerIFrame.onload = () => {
                        //https://github.com/mozilla/pdf.js/blob/master/web/app_options.js
                        pdfViewerIFrame.contentWindow.PDFViewerApplicationOptions.set("enablePermissions", true) //allow PDF documents to disable copying in the viewer
                        pdfViewerIFrame.contentWindow.PDFViewerApplicationOptions.set("defaultUrl", "") //prevent loading default pdf
                    }
                })

[PDF.js] Prevent loading default pdf

This can be done by appending ?file= to the src path, like it is mentionend here.

<!-- "?file=" prevents loading the default document -->
<iframe id="pdf-js-viewer" src="/pdf/web/viewer.html?file=" title="webviewer" frameborder="0" width="100%" height="700" allowfullscreen="" webkitallowfullscreen=""/>

Or by setting the variable defaultUrl to blank using the onload event.

pdfViewer = document.getElementById("pdf-js-viewer");

pdfViewer.onload = () => {
          pdfViewer.contentWindow.PDFViewerApplicationOptions.set(
            "defaultUrl",
            ""
          );
}; 

[nodejs] read and write a file

https://nodejs.dev/learn/reading-files-with-nodejs

https://nodejs.dev/learn/writing-files-with-nodejs

        const fs = require("fs")

        try {
            // read from local folder
            const localPDF = fs.readFileSync('PDFs/myFile.pdf')

            //write back to local folder
            fs.writeFileSync('PDFs/writtenBack.pdf', localPDF )

        } catch (err) {
            console.error(err)
        }

Converting to Base64

        try {
            // read from local folder
            const localPDF = fs.readFileSync('PDFs/myFile.pdf')
            const localBase64 = localPDF.toString('base64')

            //write back to local folder
            fs.writeFileSync(`PDFs/writtenBack.pdf`, localBase64, {encoding: 'base64'})

        } catch (err) {
            console.error(err)
        }

Reading and writing using streams with pipe

        //read and write local file
        const reader = fs.createReadStream("PDFs/myFile.pdf")
        const writer = fs.createWriteStream('PDFs/writtenBack.pdf');
        reader.pipe(writer)

[Software] Using pdfunite to merge PDF documents

First install pdfunite:

sudo apt update 
sudo apt install poppler-utils

Syntax:

pdfunite source1.pdf source2.pdf merged_output.pdf

If a pdf file is located in a different folder, you have to add the path like this: $home/Downloads/source1.pdf
If you want to merge all pdf’s of the current folder you cant type:

pdfunite *.pdf merged_output.pdf

An alternative with GUI is PDF Arranger.