Digitally Signing Documents in Windows: A Complete and Practical Guide

Today we sign documents without leaving our computers, and in Windows there are multiple ways to do so safely. From certified digital signatures to visible signatures in PDF, going through the Office signature lines or official solutions like AutoFirma, everything coexists in a single environment. Understanding what each option does, when to use it, and how to configure it correctly is key to avoiding wasting time or making mistakes.

In the following lines we gather, in simple words, all the essential information from the most reliable sources: functions of Become, Excel and PowerPoint, what exactly is a digital signature and its relationship with certificates, how to install your certificate in Windows, how to use AutoFirma for PDFs, and alternatives such as Adobe Acrobat Reader, web tools or even itself Microsoft Edge y Google Docs. The idea is that you'll leave here knowing how to choose the right tool and apply it step by step without complicating your life.

What is a digital signature and why is it important?

A digital signature is, in essence, an encrypted electronic seal that authenticates content Digital (documents, messages, macros). Its function is twofold: to link the document to the person signing it and to ensure that the content has not been modified since the signing.

For this digital signature to exist, it relies on a digital certificate linked to the signer. When sharing a signed document, Your certificate and public key travel with it, allowing recipients check the validity of the signature in front of a trusted issuing entity.

When a digital signature is valid, it provides four fundamental guarantees: authenticity of the signer, integrity of the document, non-repudiation (the signer cannot deny authorship) and, in certain contexts, certification if a secure timestamp exists.

For all this to happen, several conditions must be met: The signature must be valid, the certificate cannot be expired, the publisher or signer must be considered trustworthy and the certificate must come from a certification authority accredited.

Digital certificates and certification authorities (CA)

The digital certificate acts as your electronic identity and is used to create digital signatures. It is issued by a certification authority (CA), which acts as a notary: issues certificates, validates their validity and maintains revocation and expiration lists. Certificates typically have a limited validity period (e.g., one year), after which they are renewed or replaced.

It is possible to obtain a certificate through commercial issuing entities or organizations that provide them. There are also environments (companies, administrations) that issue their own certificates, always with the goal of making digital signatures verifiable by third parties.

From a technical point of view, the certificate provides the public key needed to validate the private key with which you sign. Thanks to this pair of keys, digital signatures can be used as a reliable method of authenticating digital information.

If you are going to share signed documents with other people and want them to be able to validate your signature without friction, the ideal is obtain a certificate from a recognized CA. There is even the possibility of creating a certificate to sign immediately; in this case, you will be able to check it in the personal certificate store from Windows (for example, from Internet Explorer: Tools > Internet Options > Content > Certificates > Personal).

Signatures in Microsoft Office: Signature and Invisible Lines

Microsoft Office allows you to work with two key concepts: Visible signature lines and insertion of invisible digital signaturesEach option meets different needs, but both can provide authenticity and protection to the document.

A signature line works as a visual marker within the document (Word or Excel) where someone is expected to sign. The author can define who should sign and add instructions; when the recipient opens the file, see the line and a notification requesting the signature.

Create a signature line in Word or Excel

To insert a signature line, place the cursor at the desired point, access the Insert tab and choose Signature line in the Text group. When you open the settings, you'll be able to fill in several details that will appear below the line.

• Suggested signer: Full name of the person who must sign.
• Title of the signer: position or function of the signatory.
• Signer's email: reference email address.
• Instructions: for example, “review the content before signing.”

Additionally, you can activate these options: allow comments when signing (to indicate the purpose of the signature) and show the date of signature next to the signature. If you need multiple lines, repeat the process as many times as you like.

Sign a signature line in Word or Excel

Signing a line combines two effects: it adds a visible representation of your signature and, at the same time, incorporates the digital signature. Just right-click on the line and choose Sign; if you're in Protected View and the file is trusted, press Edit anyway.

In the signature box you can choose three options: write down your number next to the X, sign by hand with the handwriting input function or select one image with your scanned signatureAfter choosing the method, confirm with Sign and you'll see the Signatures button appear at the bottom of the document.

Remove digital signatures in Word or Excel

If you need to remove a visible signature, open the file, right-click on the signature line and choose Remove signature. Confirm with “Yes” and the document will be left without that specific signature.

Invisible digital signatures (Word, Excel and PowerPoint)

The invisible digital signature also guarantees authenticity, integrity and origin of the document, but without showing a signature stroke. In signed files, you'll see the Signatures button at the bottom and signature details in File> Information.

To add it, open File > Info, choose the corresponding option for add a digital signature, read the program's message, confirm, and in the Sign box, indicate the purpose of the signature. Then, click Sign; the file will become read-only to prevent subsequent changes.

If you need to remove it later, go to File > Info, access the panel Authors, drop down the arrow next to the signature name and choose Remove Signature; confirm with “Yes,” and the invisible signature will be removed from the document.

Signature Apps in Windows: What to Use and When

There are two main families of tools: those you already use every day (such as Adobe Acrobat or Microsoft Word) and the specific electronic signature applicationsThe first ones are convenient if the program itself can sign the same type of document it generates.

However, this approach has clear limits: Not all applications that create documents can sign them And in many cases, the recipient will need the same application to verify the signature. That's why specific signature tools come into play, capable of sign any type of file and, in addition, available for free.

In Spain, the most popular application is AutoFirma, provided by the Public Administration. AutoFirma facilitates local document signing in desktop windows (Windows, Linux and macOS) with a graphical interface, and integrates with the Windows certificate store.

AutoFirma: secure download and installation

To download AutoFirma, it is advisable to always go to official portal of the Ministry of Economic Affairs and Digital Transformation, specifically to the section of downloads. There you will find installers for Windows (32 and 64 bits), Linux and Mac.

On a 10-bit Windows 64 computer, for example, you would download the package AutoFirma64.zip, you would unzip it and run the AutoFirma_64_v1_6_5_installer.exe installer. The wizard is very simple: follow the steps and close when finished; with that, AutoFirma will be installed and ready.

Install a digital certificate in Windows

To digitally sign you need a valid certificate (not expired). If you have it on file .p12 or .pfx, importing into Windows is straightforward: double-click on the file or right-click and “Install PFX”.

During the import wizard you can choose the warehouse: Current user (only for your user) or Local team (available to all users on the computer). Then, verify that the certificate file is correct and continue.

When the assistant asks, enter the certificate password and check the security options: enable private key protection and allow export if you wish. It is common to let Windows select the storage automatically, usually the one in Staff.

A system confirmation window may appear; accepting it will install the certificate. From that moment on, Internet Explorer, Edge y Google Chrome will be able to use it; if you use Firefox, it is advisable to install it in its own storage as well.

AutoFirma will detect the system certificate, so you can sign files without extra steps beyond choosing which certificate to use for each signature.

Sign a PDF with AutoFirma

Open AutoFirma and click "Select files to sign" to add the PDF. Since it's a PDF, the tool will offer you two options: make the signature visible within the document and/or insert a visible mark (e.g. a logo).

If you opt for visible signature, choose the page, coordinates, width and height from the signature box. You can even specify that a page be added at the end to place your signature there if you prefer.

It is possible to attach an image with your scanned handwritten signature and a descriptive text below the signature. Please note that this image is only aesthetic value; the official validity is provided by the digital signature itself. You can preview the result and save the configuration for reuse.

If you also select “Insert a visible mark”, AutoFirma will offer you choose an image as a watermark (e.g., a logo), as well as its position and which pages to apply it to. This mark can coexist with the visible signature.

When signing, select the certificate. AutoFirma will display certificates from the Windows store, although it allows you to search in Firefox or other .p12/.pfx filesDepending on the security level you have configured, you may be asked for additional confirmation or the certificate key.

Choose where to save the final PDF; by default, AutoFirma suggests the same directory and adds the “_signed” suffix to the name. Upon completion, you'll see a success message and the option to open the resulting document with your usual PDF reader.

In the reader (e.g., Adobe Acrobat Reader) you will see the signature visible and the markup if you inserted it. In addition, the viewer will display a message indicating that the document is signed and the signatures are validFrom the signature panel, you can view the details of the signature and the certificate used.

Sign PDFs with Adobe Acrobat Reader DC

The free version of Adobe Acrobat Reader includes the tool Fill in and sign, accessible from the Tools tab. Open it with your PDF uploaded to begin the process.

If this is your first signature, create a new one from the Sign > Add Signature button. You can write your name, draw it with a mouse or tablet, or upload an image with your signature. When you're happy with the result, click Apply.

The cursor will change to the signature block and you will be able to place it in the exact spot of the document where it should go. To lock it, click. From there, save the signed file (File > Save), and if you want to keep the original intact, use “Save As” with a different name.

Sign PDFs from the web with Smallpdf

If you prefer an online service, go to Smallpdf and upload your document with Choose fileCreating your signature is flexible: you can draw it, upload an image, or use your camera to capture it.

Draw your signature in the box and when you're satisfied, press Save. Then, return to the document and choose Place Signature to select your signature from the list (you can have several ready if you need to).

Place the signature in the desired location and adjust its size and scale with the available controls. To finish, click APPLY; the system will generate the signed PDF in a few seconds, and you can download it by clicking "Download file now."

Open the result with your PDF reader or even with Google Chrome or Microsoft Edge to check that the signature is in place and displayed correctly.

Sign in without installing anything: Microsoft Edge

If you don't want to install additional software, Windows provides a quick way out with Microsoft Edge. Open the PDF in Edge (double-click if it's your default viewer, or Open with> Microsoft Edge) and go to the Draw icon in the top bar.

Activate the pencil or pen, adjust the thickness and color, and sign in the corresponding place. When you're done, turn off drawing mode and save the PDF with the save or "Save As" icon. This is a signature drawn on the document, useful for simple needs where cryptographic validation is not required.

Another online alternative: Google Docs

If you don't mind uploading the document to the cloud, you can upload the PDF to Google Drive, right-click and open it with Google Docs. The system will convert the PDF to an editable document, although the layout may vary depending on your needs. complex tables or images.

To sign, insert an image of your signature (Insert > Image > Upload from computer) or create one from Insert > Drawing > New with the option Freehand line. Draw, adjust thickness and color, and click “Save & Close.”

Once you have the signature on the document, place it and resize it if necessary to make it look natural. Finally, download the result as PDF document from File > Download > PDF Document.

More information and useful resources

If you are interested in more details about how signatures work in Office, how to protect messages in Outlook with a digital ID or where to find digital ID services, there are official resources and complementary guides. In some cases, you will also find PDF documentation on signature processes in Adobe Acrobat Reader DC or guides for using public administration tools.

Remember that signatures in Word, Excel and PowerPoint can be visible through signature lines or invisible, and in both cases the Signatures button and the Information section of the File tab provide the status and details. AutoFirma, on the other hand, allows you to sign any type of file and works natively with the Windows certificate store, simplifying the process.

As for visible signatures within PDFs, you can combine a signature box with image and text and, if needed, a visible mark in the form of a logo or seal. Don't forget that the legal force is provided by the digital signature backed by the certificate, while the image of the signature serves a more aesthetics and location.

With all of the above you have covered the panorama of digitally signing documents in Windows: understand what a digital signature is and its guarantees, know the relationship with certificates and CAs, master Office options (signature lines and invisibles), choose well between everyday programs and specific tools such as AutoFirma and, finally, manage alternatives such as Adobe Acrobat Reader, web services, Edge, or Google Docs depending on what suits you at any given time.