In addition, PDF-compressed objects can have their own additional encodings and compressions.īy decompressing, we end up with a file much like the pure-text sample PDF from earlier.
Compression is a method to reduce the size of a PDF file via specific encodings that can convert a pure-text object to a binary stream, thereby sometimes rendering the source PDF operators obfuscated. The same goes for many open-source tools, which use any of the libraries we discuss here. Thus, it’s up to the creator of the original content as well as their tool of choice to save or export the file in a given way.įor example, some Adobe products offer options to save a PDF decompressed or uncompressed, i.e., without compression. Still, how can we convert the operators of a PDF file and as much of its content as possible to editable ASCII text?ĭue to the format’s ubiquity, many tools can generate PDF files. Of course, other objects like media might not have a purely textual representation. Without seeing the commands, it’s much harder to modify them. Here, we begin a text segment at BT, change the current font via Tf and write Hello World with Tj, before ending the text segment at ET. However, we’re no longer able to directly see or edit the PDF’s previous contents: 4 0 obj In this case, we see object 4 0 is an encoded stream in a binary representation (here, flate), which makes the file smaller. For example, we can have the sample PDF file from earlier, but in binary form: %PDF-1.1 Often, a pure-text representation is unusual.
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These serve as a hint to processing software that a PDF file is best read as binary data. The optional second line of PDF files often contains several non- ASCII characters like %¥±ë. Moreover, we can use object references such as 2 0 R and 3 0 R. Also, the latter assigns an array to /MediaBox, which is similar to a page size. Let’s create a sample pure-text PDF: %PDF-1.1įor example, this simple blank PDF has four objects:Įach of these objects has a dictionary ( >) of key-value pairs like /Type /Page and /MediaBox. This collection of objects is the format’s backbone and plays a key role in the presentation, so its structure is well-defined. Essentially, PDF files consist of pages, described by objects.
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