OmniDocmisunderstanding 1: 1a is "high quality"
Explain the meaning of codes such as 1a, 2b, 3u in the name of PDF/A: the numbers are standard versions, and the letters are compliance levels. Explain the requirements for text, structure, and fonts for each level, and give methods for selecting them based on use.
#What do the PDF/A-1a and PDF/A-2b grade codes mean respectively?
Key points of this article
- The numbers are the standard versions of PDF/A (1, 2, 3, 4) and the letters are the compliance levels (a, b, u), viewed separately.
- The letter b only ensures a stable appearance, but does not ensure that the text is searchable; choose u when you need to search and copy text, and choose a when you need an accessible structure.
- Level a has strict requirements, including all the requirements of u and b, and does not mean "higher image quality".
- The scanned document must be OCRed first, otherwise the text will still not be searchable after it is converted to PDF/A.
- Just because the file name says PDF/A-2b does not mean it is compliant, try to check it with a verification tool.
When many people export or convert PDF, they will see names like PDF/A-1a, PDF/A-2b, and PDF/A-3u in the options. They don’t know what the numbers and letters behind them mean, and they don’t know which one to choose. This type of code name generally appears in scenarios that require long-term archiving, government submission, library collection, or academic submission. If you select the wrong level, the common result is that the file can be opened, but the words cannot be found, or it does not comply with the rules when being verified.
This article is written for people who need to convert PDF/A but cannot understand the code names. After reading, you will be able to distinguish what numbers and letters represent, know the differences between 1a, 2b, and 3u, select the appropriate level according to your own use, and then use a simple process to check the results.
Which level should I choose, 1a or 2b? One sentence conclusion
The number determines which version of the PDF standard is based on, and the letter determines how strict the compliance requirements are. When choosing, don't think bigger numbers are better, but think about how your file needs to be used. The following is a judgment table for common situations:
| your situation | Recommended practices | reason |
|---|---|---|
| It only requires that the layout remains unchanged for a long time. It doesn’t matter whether the text can be searched or not. | 1b or 2b | Only ensure stable appearance, with lower requirements on structure and text mapping |
| Need to copy text and search full text | 2u or 3u | Each character must have a Unicode mapping so that text can be extracted correctly |
| Accessible reading is required, such as screen reading software to read titles and paragraphs | 2a or 3a | Requires tagged structure and reading order while meeting the requirements of u |
| The original is a scanned picture | Do OCR first, then choose 2u or 2a | There is no mappable text in the scanned image, and the search still fails without recognition and conversion. |
| Attachments in other formats need to be embedded | 3 series | PDF/A-3 allows embedding of files of any format, 1 and 2 do not |
If your organization or submission system specifies a specific level, the specified level shall prevail. The above table is for reference only.
PDF/A How to split the name: the number is the version and the letter is the level
PDF/A is a subset of PDF designed for long-term preservation, so that files can still be opened and displayed in the same way many years later. Its name consists of two parts:
- Number (1, 2, 3, 4): Standard version. 1 Based on the older PDF 1.4 specification; 2 Based on PDF 1.7; 3 Builds on 2 to allow embedding of files in other formats; 4 Based on PDF 2.0. The larger the number, usually the newer the feature, but it doesn’t mean which version is more suitable for you.
- Letter (a, b, u): Compliance level. ; b (Basic, basic level) : Ensure that the appearance of the page can be reliably reproduced, fonts must be embedded, and there are clear rules for color and transparency. ; u (Unicode) : Based on b, each character is required to be mapped to Unicode, so the text can be copied and searched. ;a (Accessible, accessibility level): Based on u, the file is required to have a tag structure, logical sequence and readable text information to facilitate the use of assistive technologies.
So 2a contains the requirements of 2u, which in turn contains the requirements of 2b. The letters are gradually tightened, rather than three independent "image qualities". The base version of PDF/A-4 has no letter suffix, and there are variants for project and embedded files.
Common misunderstanding: 1a does not mean trying your best, and 2b does not mean updating.
There are several areas of confusion surrounding these code names:
The "a" in 1a refers to the structure and accessibility requirements and has nothing to do with image clarity and color reproduction. 1a requires more content than 1b, so it is more difficult to generate and verify. It does not mean that the display effect is better. If you only need to save the layout for a long time, 1b or 2b will be enough.
misunderstanding 2: 2b is better than 1b, so choose 2b directly
2b is based on the newer standard version, but the requirements of "b" are not much higher than 1b. Version upgrades bring mainly functional support, such as transparency and more compression. Whether you choose 2b or not depends on whether your receiver can handle the corresponding version, not just the numbers.
misunderstanding 3: files with b can be searched
This is a common misunderstanding. Level b only ensures appearance, not text can be extracted. If your files need to be searched, copied or read by other software, choose the level with u. This is the reason why many people find that "search cannot be opened" after conversion.
misunderstanding 4: if the file name is PDF/A-2b, it must comply with the regulations.
The name is just a declaration, and there may be unembedded fonts, encryption, scripts, or external links inside the file, which can lead to non-compliance. You need to check with a special verification tool instead of just looking at the file name.
# Core comparison
| Grade | Stable appearance | Text can be searched and copied | Tagged structure | Typical use |
|---|---|---|---|---|
| b | Request | There is no guarantee | Do not require | Only need to save the layout file for a long time. |
| u | Request | Request | Do not require | Archived materials that require full-text retrieval |
| a | Request | Request | Request | Official documents that require accessibility |
The table only shows the scope of requirements for each level. When making a choice, answer clearly the two questions of "whether you need to search" and "whether you need accessibility", and the level is basically set.
# how to use it
If you have a document that needs to be transferred to PDF/A, you can process it in the following order:
- First determine whether the original file is scanned or not. In PDF, try to select a piece of text with the mouse, but you can only select the whole page of the picture, usually the scanned piece.
two. OCR the scanned piece first. OCR the scanned version of PDF in the PDF editor of the OmniDoc desktop client so that the text can be selected. OCR results need to be checked paragraph by paragraph, especially numbers, formulas and proper nouns.
- Determine the level. According to the previous judgment table, make it clear that you need b, u or a, and which version to use.
- Export PDF/A. The functions currently provided by OmniDoc do not include exporting PDF/A directly, so this step can be done by using desktop office software to export PDF/A-related options when exporting PDF, or to convert websites online. Before using an online site, confirm its privacy policy and do not upload confidential or undisclosed files.
- Check with the calibration tool. Use a special PDF/A check tool to confirm that the level is really up to standard, and check whether the font is embedded and whether the text can be copied.
- Check the content. The conversion process may change typesetting or characters, open the file before formal submission, and review the key content page by page.
If your documents need to be translated before archiving, it is recommended to complete the translation first, check the translation correctly, and then carry out the above conversion and verification. The results of machine translation need to be checked manually, especially terms and numbers.
# which method is suitable for you?
Just want to keep the contract and specification on file for a long time, no need to search: select level b, check the font embedded. -to put the research report in a searchable database: select level u and make sure that the text can copy the search. -to submit to units that need accessibility support: select level an and check the title and reading order. -the scanned piece in hand: OCR first, and then select the grade, otherwise the following steps will be affected.
# frequently asked questions (FAQ)
1. Can PDF/A-1a be directly converted to PDF/A-2b?
You can regenerate it with a conversion tool, but the transformation is a re-output from the content, not a simple change to the tag. After the conversion, you still need to check with the verification tool to make sure that the layout and text are normal.
2. Why did I choose PDF/A-2b, the file still can't find a word?
2B only requires a stable appearance and does not require text mapping. When you need to search, you should select 2u or 2a and confirm that the original file itself has extractable text.
3. After the scanned piece is converted to PDF/A, why can't the text be selected?
The content of the scanned piece is a picture, the conversion only changes the format, and the text message is not generated. First do OCR to identify the text, and then convert it to get a searchable PDF/A.
4. What's the difference between 1a and 2a? Which one should I choose?
Both require structural and accessible information, the difference lies in the standard version on which they are based. 2a based on the newer version, compatibility is usually sufficient; if the recipient explicitly requests a version, the request of the other party shall prevail.
5. What do I need to check after the conversion?
Check whether the level is checked, whether the font is embedded, whether the text can be copied, and whether the typesetting and content of key pages are consistent with the original text.
# Summary
The numbers in the PDF/A name represent the standard version, the letters indicate the compliance level, where b only ensures the appearance, u ensures that the text is searchable, and an also requires an accessible structure. When selecting a grade, first look at how the file is used, the scanned piece should be OCR first, and then check with the verification tool after conversion, so that the PDF/A document can really meet the needs of archiving.
