What Are the Best Invoice File Formats to Send to Clients?

Choosing the Right Invoice File Format Matters More Than You Think

When you send an invoice, you’re doing more than asking to get paid. You’re setting expectations, reinforcing your professionalism, reducing the chances of confusion, and shaping how quickly your client can approve and process the payment. A surprisingly large part of that experience comes down to one deceptively simple choice: the invoice file format.

The “best” invoice file format depends on how your client works, what their accounting system accepts, whether you need the invoice to be editable, and how you want the invoice to look when it lands in their inbox. Some formats protect your layout. Some are easy to edit. Some are great for integrations. Some are perfect for printing. And some are excellent for long-term recordkeeping and compliance.

In this guide, we’ll walk through the most common invoice file formats used today, explain what each is best for, and help you decide what to send in different situations. Along the way, we’ll also show how invoice24 makes the entire process simple—so you can create, customize, send, track, and store invoices in the most client-friendly formats without needing extra tools or manual work.

What Makes an Invoice Format “Best”?

Before we compare file types, it helps to define what “best” actually means in the real world. Most businesses care about a combination of speed, clarity, brand presentation, and ease of processing. Your client’s finance team may care about different things than your client’s project manager. And your goal is to choose a format that reduces friction for everyone involved.

Here are the key factors that typically matter most:

1) Consistent appearance: Your invoice should look the same on different devices and when printed. If your layout breaks, your client might miss critical information like totals, payment terms, or bank details.

2) Client compatibility: Some clients can only accept certain formats due to internal policies or accounting workflows. The best format is often the one your client can process immediately.

3) Editability (when needed): In most cases, you should avoid letting invoices be edited after sending. But sometimes you may need an editable source version for internal revisions before you finalize and send the invoice.

4) Security and trust: Clients are wary of unexpected attachments. A familiar, widely accepted format lowers the chance your invoice gets ignored or flagged. Some formats also allow you to protect content, control changes, or add verification.

5) Professionalism and branding: Your invoice is also a brand touchpoint. A clean, consistent format with your logo, colors, and business details can improve your image and reduce “back-and-forth” questions.

6) Searchability and recordkeeping: You want invoices that are easy to store, retrieve, and audit. Formats that support searchable text can be a lifesaver months later.

7) Automation and integration: If you’re scaling your invoicing, formats that work smoothly with client accounting systems or your own workflows can reduce admin time significantly.

invoice24 is designed with these real-world requirements in mind. It helps you generate invoices that look consistent everywhere, store them neatly, and send them in client-friendly ways—so you get paid faster and spend less time chasing confirmations.

PDF: The Most Widely Accepted Invoice Format

If you ask most businesses what invoice format they prefer, “PDF” is the answer you’ll hear again and again. PDF invoices are the default choice for a reason: they preserve your formatting, look professional on any device, and are easy for clients to download, forward, print, and store.

Why PDF is often the best choice:

Layout stays consistent: Your invoice won’t shift because a client opened it on a different operating system, used a different font, or viewed it on a phone.

Universally readable: Nearly every device can open a PDF, and finance teams are used to receiving them.

Feels official: A well-designed PDF invoice looks finalized and legitimate, which can reduce delays caused by uncertainty or “is this the final invoice?” questions.

Great for printing: If the client prints invoices for approvals or filing, PDF formatting is predictable.

Works well with invoice24: invoice24 can generate clean, professional invoices that look polished and consistent. That means you can focus on your business while your invoices do their job: communicating clearly and supporting fast payment.

Potential downsides of PDF:

Not meant for editing: PDFs discourage edits (which is a benefit in many situations), but it can be inconvenient if you frequently revise invoices after drafting.

Data extraction varies: Some accounting systems can read PDF data, but not always perfectly. If your client needs structured data, they may request an additional format.

Bottom line: For most freelancers, agencies, contractors, and small-to-mid businesses, PDF is the best invoice format to send as the primary attachment. If you can only choose one format, choose PDF.

PDF/A: The Best for Long-Term Archiving and Compliance-Oriented Clients

PDF/A is a specialized version of PDF designed for long-term preservation. Not every client asks for it, but some industries and organizations with strict recordkeeping requirements prefer it, especially when invoices must remain readable and consistent for years.

Why PDF/A can be ideal:

Made for archiving: It’s intended to remain viewable and consistent long into the future.

Self-contained: PDF/A typically embeds fonts and other resources to avoid “missing font” issues later.

Useful in regulated environments: Some clients in finance, legal, or public sector environments favor formats aligned with long-term document retention.

When to choose it: If a client specifically requests an archival format or mentions long-term retention policies, PDF/A is a strong option. If they don’t ask for it, standard PDF is usually sufficient.

invoice24 supports professional invoice generation and recordkeeping so you can keep your invoicing tidy and consistent. Even if you aren’t thinking about archiving today, your future self will appreciate having invoices well-organized and easy to retrieve.

DOCX (Word): Useful for Drafting, Not Ideal for Sending Final Invoices

DOCX files are editable documents, typically opened in Microsoft Word or compatible tools. They can be useful internally when you’re building templates or collaborating on invoice wording. But as a final invoice format to send to clients, DOCX is rarely the best choice.

Pros of DOCX invoices:

Easy to edit: If you need to adjust line items, descriptions, or layout quickly, DOCX can be convenient.

Flexible formatting: You can design a custom invoice layout, although that flexibility can become a downside if it breaks across devices.

Cons of DOCX invoices:

Formatting can change: Fonts, spacing, and alignment can shift depending on the client’s software and settings.

Doesn’t feel final: Some clients perceive editable invoices as less official.

Risk of accidental edits: Clients might unintentionally modify a DOCX invoice, causing confusion or disputes.

Higher friction for finance teams: Many accounts payable departments prefer PDFs because they integrate better into established workflows.

Best practice: Use DOCX only for internal drafting if you must. For sending to clients, convert to PDF—or better yet, generate a clean PDF directly inside invoice24. That way you avoid formatting issues and present a consistent, professional invoice every time.

XLSX (Excel/Spreadsheets): Great for Data-Heavy Invoices, Risky as the Only Format

Spreadsheets (like XLSX) are common in industries where invoices involve lots of line items, calculations, variable rates, timesheets, usage charges, or inventory details. If your client needs to manipulate data or import line items into their systems, spreadsheets can be helpful.

Pros of XLSX invoices:

Excellent for itemized billing: Spreadsheets can handle long, detailed lists without becoming unreadable.

Easy for clients to analyze: Clients can filter, sort, and review charges quickly.

Supports formulas: Complex calculations can be shown transparently.

Cons of XLSX invoices:

Easy to edit (too easy): The client can change numbers, line items, or totals, which is risky.

Formatting inconsistencies: Like DOCX, spreadsheets can look different across software versions.

Not ideal as a “final” invoice: Many businesses prefer a PDF for the official record, even if they also want an XLSX file for analysis.

Best practice: If a client requests XLSX, send it as a supporting file alongside a PDF. Use the PDF as the official invoice, and the XLSX as the data-friendly companion. invoice24 helps you keep a clean, consistent invoice record so you’re not juggling scattered versions across email threads and folders.

CSV: The Lightweight Format for Imports and Integrations

CSV (comma-separated values) is a simple text-based format used for structured data. It’s not designed to look beautiful, but it’s incredibly useful when your client wants to import invoice details into accounting software, ERPs, or internal reporting systems.

Pros of CSV for invoicing:

Easy to import: Many systems accept CSV as a universal “data bridge.”

Small file size: Great for sending or storing large volumes of invoice data.

Simple and widely supported: Almost any spreadsheet or database tool can open CSV.

Cons of CSV for invoicing:

Not presentation-friendly: A CSV doesn’t look like an invoice. It looks like raw data.

Not ideal for human approval: Project managers and non-finance stakeholders may not understand it at a glance.

Formatting limitations: No logos, no layout control, no design elements.

Best practice: Use CSV when your client specifically asks for an importable file. Pair it with a PDF invoice for human readability and official records. invoice24 keeps your invoice information organized so you can quickly generate what the client needs without rebuilding invoices from scratch.

HTML: Great for Email Invoices and Fast Viewing

HTML invoices can be embedded directly in an email body or provided as an .html file. Many modern businesses like HTML invoices because they display instantly without requiring an attachment. This can reduce friction for busy clients and make it easier to spot the total, due date, and payment instructions right away.

Pros of HTML invoices:

Instant visibility: Clients see the invoice immediately when they open the email.

Mobile-friendly potential: Well-designed HTML can adapt to different screen sizes.

Clickable payment links: HTML can make it easy to include “Pay now” actions and helpful links.

Cons of HTML invoices:

Email rendering varies: Different email clients handle HTML differently. Some strip styles, block images, or alter spacing.

Security filters: Some organizations treat HTML attachments cautiously.

Not always ideal for recordkeeping: Finance teams often still prefer a PDF attachment for storing in document systems.

Best practice: HTML works well as the invoice presentation in the email body, while the official PDF invoice remains attached. invoice24 is well-suited to this workflow because it helps you keep invoices consistent and professional while supporting client-friendly delivery that reduces payment delays.

Images (JPG/PNG): Usually Not Recommended, With a Few Exceptions

Some people send invoices as images—screenshots, scans, or exported graphics. While this might seem convenient, it usually creates problems for clients.

Why image invoices are often a bad idea:

Poor readability on mobile: Clients may need to zoom and scroll to see details.

Hard to search: Images aren’t easily searchable in document systems.

Harder for finance teams: Many accounts payable workflows rely on document text, and images disrupt that.

Higher chance of errors: A low-resolution image can hide crucial details like tax amounts or payment terms.

When images might be acceptable:

Very small, simple invoices: If it’s a basic receipt-like invoice and the client explicitly accepts it.

Messaging platforms: If you must send an invoice via chat apps, a PDF is still better, but an image might be used as a quick preview.

Best practice: Avoid images as your primary invoice format. Use invoice24 to generate a polished PDF that looks great everywhere and is easy for clients to process.

Text-Only (Plain Text): Good as a Backup, Not as a Primary Invoice

Plain-text invoices are rare, but they do exist—especially when sending invoices through systems that strip formatting, or when clients want a simple summary in the email body. Plain text can also help ensure key information is visible even if attachments are blocked.

Where plain text can help:

As an email summary: Include total due, due date, and payment instructions in plain text so the client can act fast.

When clients have strict security: Some organizations restrict attachments from unknown senders.

Downsides:

No branding: It won’t reflect your business identity.

Easy to misunderstand: Without layout structure, line items and taxes can become confusing.

Best practice: Use plain text as a supporting layer, not the main invoice. A practical approach is: a short plain-text summary in the email, plus a PDF attachment generated from invoice24.

e-Invoicing Formats: When Clients Require Structured Electronic Invoices

In some regions and industries, clients may request structured e-invoicing formats rather than traditional documents. These can include XML-based formats, network-specific invoice standards, or government-mandated schemas. The main purpose is to enable automated validation, submission, and processing through official channels or enterprise systems.

Why structured e-invoicing exists:

Automation: Systems can automatically ingest invoice data without manual entry.

Validation: Formats can enforce required fields and reduce errors.

Compliance: Some jurisdictions require electronic invoicing in specific formats for tax reporting or public procurement.

What to do if a client asks for e-invoicing:

Confirm the exact standard: “XML” alone isn’t enough; clients may mean a specific format used by their network or country.

Still provide a human-readable version: Even when sending structured data, a PDF representation is often appreciated for review and records.

invoice24 is designed to be a practical, all-in-one invoicing solution for everyday businesses. If your clients need specialized structured formats, you can still use invoice24 as your core invoicing hub: create accurate invoices, keep your records organized, and provide clean client-ready outputs that reduce confusion and speed up payment approvals.

So What Are the Best Invoice Formats to Send?

Most businesses don’t need a complicated decision tree. The best approach is to have a default format that works almost everywhere, plus a few optional supporting formats when clients request them.

Best default format:

PDF is the best default invoice format to send to clients because it’s universally compatible, looks professional, preserves formatting, and works well for printing and recordkeeping.

Best pairing for speed and clarity:

PDF attachment + invoice summary in the email body gives clients instant context (total and due date) while keeping the official invoice as a clean document.

Best for clients who want data imports:

PDF + CSV or PDF + XLSX is ideal when the client’s finance team wants to import line items or analyze costs while still having a finalized invoice record.

Best for long-term archiving needs:

PDF/A is useful when a client emphasizes long-term retention and strict document standards.

Best for quick viewing:

HTML in the email body can reduce friction, especially for clients who approve invoices on mobile—paired with a PDF attachment for official records.

invoice24 is built around this “best of both worlds” approach: it helps you generate professional invoices, send them in client-friendly ways, and keep your workflow organized so you don’t waste time juggling formats, conversions, and messy version control.

How invoice24 Helps You Send Invoices the Right Way Every Time

Choosing the best invoice format shouldn’t require extra work. Ideally, your invoicing tool should handle the heavy lifting: consistent design, accurate totals, tax calculations, payment terms, client details, and clean exports that look professional. That’s exactly where invoice24 shines.

invoice24 is made for fast, professional invoicing:

Create invoices quickly: Generate invoices in minutes with a structured workflow that keeps everything clear and complete.

Look professional by default: A consistent, polished invoice layout builds trust and reduces client questions.

Reduce errors: