At some point in life, you must have wondered if was possible to digitally sign a document without buying expensive software or service from a third party. It turns out that you can quite easily, but very few people actually know about this.

First you need a "digital ID". This is the equivalent of a pen in the real world. It is used to create a digital signature just as a pen would be used to create one with ink on a piece of paper. So a digital ID creates your digital signature on an electronic document. With this you can digitally sign any electronic data, but for simplicity we will limit this to a PDF file using Adobe Reader.

You no longer need to go through the entire laborious process of printing a document, signing it, and scanning it back again to email it. Everybody has Adobe Reader installed in his or her computer. The first step is to ensure that you have the latest version. Open Reader, click on Help on the menu bar and check for updates.

Open the document you want to digitally sign with Adobe Reader. Assuming you have version XI of Reader, click on Fill & Sign on the top right of the screen. Expand 'Work with Certificates' and click on 'Sign with Certificate'. Click on the button for 'Drag New Signature Rectangle'. The mouse pointer will change to enable you to draw a rectangle. After you draw the signature box you will get the option to create a digital ID. Opt to create a new digital ID and click on Next. Select 'New PKCS #12 digital file' and click on Next.

Now you will be asked to enter your name and email address. Change the country to India, but do not change any other fields. Click on Next. Enter a password. This password will be needed to access your signature in the future. So do not forget it. Click on Finish. Once your signature is added to the document, you will need to save it. Now you can email this document. The recipient of this document only needs to click on the Signature panel in Reader to validate the document. He will know whether the document was modified or not after it was signed, who signed it and at what time.

If you prefer signing your document the old fashioned way, you could do that too. Sign a piece of paper and hold it up to your computer's webcam. Adobe Reader will capture that signature and turn it into a digital image, allowing you to easily apply it to PDF documents in future. You only need to capture your signature once in this way. For this you will need to click on Fill & Sign-Fill & Sign Tools-Place Signature in Reader.

On a Mac it is even easier. Open the documents with OS X's Preview application. MacBooks have excellent trackpads. You can actually draw your signature on the trackpad with a finger to enter it into Preview.

You could also just sign a piece of paper and hold it up to the built-in camera. Before doing this open the document in Preview and click on the icon for signature and select Camera. That's it. If you are drawing a signature select Trackpad.

It is also pretty easy signing a document on a phone or tablet download on both iOS and Android. Download Adobe Acrobat Reader. Long press on the PDF document and you will get the option to add a signature. You don't have to sign up to an Adobe account or pay anything extra.

Send in your computer-related problems to askdoss@abpmail.com with bits&bytes as the subject line